OpenVPN Management Interface Notes ---------------------------------- The OpenVPN Management interface allows OpenVPN to be administratively controlled from an external program via a TCP or unix domain socket. The interface has been specifically designed for developers who would like to programmatically or remotely control an OpenVPN daemon, and can be used when OpenVPN is running as a client or server. The management interface is implemented using a client/server TCP connection or unix domain socket where OpenVPN will listen on a provided IP address and port for incoming management interface client connections. The management protocol is currently cleartext without an explicit security layer. For this reason, it is recommended that the management interface either listen on a unix domain socket, localhost (127.0.0.1), or on the local VPN address. It's possible to remotely connect to the management interface over the VPN itself, though some capabilities will be limited in this mode, such as the ability to provide private key passwords. The management interface is enabled in the OpenVPN configuration file using the following directive: --management See the man page for documentation on this and related directives. Once OpenVPN has started with the management layer enabled, you can telnet to the management port (make sure to use a telnet client which understands "raw" mode). Once connected to the management port, you can use the "help" command to list all commands. COMMAND -- bytecount -------------------- The bytecount command is used to request real-time notification of OpenVPN bandwidth usage. Command syntax: bytecount n (where n > 0) -- set up automatic notification of bandwidth usage once every n seconds bytecount 0 -- turn off bytecount notifications If OpenVPN is running as a client, the bytecount notification will look like this: >BYTECOUNT:{BYTES_IN},{BYTES_OUT} BYTES_IN is the number of bytes that have been received from the server and BYTES_OUT is the number of bytes that have been sent to the server. If OpenVPN is running as a server, the bytecount notification will look like this: >BYTECOUNT_CLI:{CID},{BYTES_IN},{BYTES_OUT} CID is the Client ID, BYTES_IN is the number of bytes that have been received from the client and BYTES_OUT is the number of bytes that have been sent to the client. Note that when the bytecount command is used on the server, every connected client will report its bandwidth numbers once every n seconds. When the client disconnects, the final bandwidth numbers will be placed in the 'bytes_received' and 'bytes_sent' environmental variables as included in the >CLIENT:DISCONNECT notification. COMMAND -- echo --------------- The echo capability is used to allow GUI-specific parameters to be either embedded in the OpenVPN config file or pushed to an OpenVPN client from a server. Command examples: echo on -- turn on real-time notification of echo messages echo all -- print the current echo history list echo off -- turn off real-time notification of echo messages echo on all -- atomically enable real-time notification, plus show any messages in history buffer For example, suppose you are developing a OpenVPN GUI and you want to give the OpenVPN server the ability to ask the GUI to forget any saved passwords. In the OpenVPN server config file, add: push "echo forget-passwords" When the OpenVPN client receives its pulled list of directives from the server, the "echo forget-passwords" directive will be in the list, and it will cause the management interface to save the "forget-passwords" string in its list of echo parameters. The management interface client can use "echo all" to output the full list of echoed parameters, "echo on" to turn on real-time notification of echoed parameters via the ">ECHO:" prefix, or "echo off" to turn off real-time notification. When the GUI connects to the OpenVPN management socket, it can issue an "echo all" command, which would produce output like this: 1101519562,forget-passwords END Essentially the echo command allowed us to pass parameters from the OpenVPN server to the OpenVPN client, and then to the management interface client (such as a GUI). The large integer is the unix date/time when the echo parameter was received. If the management interface client had issued the command "echo on", it would have enabled real-time notifications of echo parameters. In this case, our "forget-passwords" message would be output like this: >ECHO:1101519562,forget-passwords Like the log command, the echo command can atomically show history while simultaneously activating real-time updates: echo on all The size of the echo buffer is currently hardcoded to 100 messages. Generally speaking, the OpenVPN Core does not understand echo messages at all (so a cooperating GUI and Server can use this mechanism for arbitrary information transport). This said, a few echo commands have been agreed upon between the community maintained OpenVPN Windows GUI and Tunnelblick for MacOS, and documentation of these can be found in doc/gui-notes.txt. COMMAND -- exit, quit --------------------- Close the management session, and resume listening on the management port for connections from other clients. Currently, the OpenVPN daemon can at most support a single management interface client any one time. COMMAND -- help --------------- Print a summary of commands. COMMAND -- hold --------------- The hold command can be used to manipulate the hold flag, or release OpenVPN from a hold state. If the hold flag is set on initial startup or restart, OpenVPN will hibernate prior to initializing the tunnel until the management interface receives a "hold release" command. The --management-hold directive of OpenVPN can be used to start OpenVPN with the hold flag set. The hold flag setting is persistent and will not be reset by restarts. OpenVPN will indicate that it is in a hold state by sending a real-time notification to the management interface client, the parameter indicates how long OpenVPN would wait without UI (as influenced by connect-retry exponential backoff). The UI needs to wait for releasing the hold if it wants similar behavior: >HOLD:Waiting for hold release:10 Command examples: hold -- show current hold flag, 0=off, 1=on. hold on -- turn on hold flag so that future restarts will hold. hold off -- turn off hold flag so that future restarts will not hold. hold release -- leave hold state and start OpenVPN, but do not alter the current hold flag setting. COMMAND -- kill --------------- In server mode, kill a particular client instance. Command examples: kill Test-Client -- kill the client instance having a common name of "Test-Client". kill 1.2.3.4:4000 -- kill the client instance having a source address and port of 1.2.3.4:4000 Use the "status" command to see which clients are connected. COMMAND -- log -------------- Show the OpenVPN log file. Only the most recent n lines of the log file are cached by the management interface, where n is controlled by the OpenVPN --management-log-cache directive. Command examples: log on -- Enable real-time output of log messages. log all -- Show currently cached log file history. log on all -- Atomically show all currently cached log file history then enable real-time notification of new log file messages. log off -- Turn off real-time notification of log messages. log 20 -- Show the most recent 20 lines of log file history. Real-time notification format: Real-time log messages begin with the ">LOG:" prefix followed by the following comma-separated fields: (a) unix integer date/time, (b) zero or more message flags in a single string: I -- informational F -- fatal error N -- non-fatal error W -- warning D -- debug, and (c) message text. COMMAND -- mute --------------- Change the OpenVPN --mute parameter. The mute parameter is used to silence repeating messages of the same message category. Command examples: mute 40 -- change the mute parameter to 40 mute -- show the current mute setting COMMAND -- net -------------- (Windows Only) Produce output equivalent to the OpenVPN --show-net directive. The output includes OpenVPN's view of the system network adapter list and routing table based on information returned by the Windows IP helper API. COMMAND -- pid -------------- Shows the process ID of the current OpenVPN process. COMMAND -- password and username -------------------------------- The password command is used to pass passwords to OpenVPN. If OpenVPN is run with the --management-query-passwords directive, it will query the management interface for RSA private key passwords and the --auth-user-pass username/password. When OpenVPN needs a password from the management interface, it will produce a real-time ">PASSWORD:" message. Example 1: >PASSWORD:Need 'Private Key' password OpenVPN is indicating that it needs a password of type "Private Key". The management interface client should respond as follows: password "Private Key" foo Example 2: >PASSWORD:Need 'Auth' username/password OpenVPN needs a --auth-user-pass username and password. The management interface client should respond: username "Auth" foo password "Auth" bar The username/password itself can be in quotes, and special characters such as double quote or backslash must be escaped, for example, password "Private Key" "foo\"bar" The escaping rules are the same as for the config file. See the "Command Parsing" section below for more info. The PASSWORD real-time message type can also be used to indicate password or other types of authentication failure: Example 3: The private key password is incorrect and OpenVPN is exiting: >PASSWORD:Verification Failed: 'Private Key' Example 4: The --auth-user-pass username/password failed, and OpenVPN will exit with a fatal error if '--auth-retry none' (which is the default) is in effect: >PASSWORD:Verification Failed: 'Auth' Example 5: The --auth-user-pass username/password failed, and the server provided a custom client-reason-text string using the client-deny server-side management interface command. >PASSWORD:Verification Failed: 'custom server-generated string' Example 6: If server pushes --auth-token to the client, the OpenVPN will produce a real-time PASSWORD message: >PASSWORD:Auth-Token:foobar Example 7: Static challenge/response: >PASSWORD:Need 'Auth' username/password SC:1,Please enter token PIN OpenVPN needs an --auth-user-pass username and password and the response to a challenge. The user's response to "Please enter token PIN" should be obtained and included in the management interface client's response along with the username and password formatted as described in the Challenge/Response Protocol section below. Example 8: Dynamic challenge/response: >PASSWORD:Verification Failed: ['CRV1:R,E:Om01u7Fh4LrGBS7uh0SWmzwabUiGiW6l:Y3Ix:Please enter token PIN'] The previous --auth-user-pass username/password failed or is not fully complete, and the server provided a custom client-reason-text string indicating that a dynamic challenge/response should occur the next time that a "Need 'Auth' username/password" message is seen. When the next "Need 'Auth' username/password" without a static challenge is seen, the user's response to "Please enter token PIN" should be obtained and included in the management interface client's response along with the username and password formatted as described in the Challenge/Response Protocol section below See the "Challenge/Response Protocol" section below for more details about examples 7 and 8, including how the management interface client should respond. COMMAND -- forget-passwords --------------------------- The forget-passwords command will cause the daemon to forget passwords entered during the session. Command example: forget-passwords -- forget passwords entered so far. COMMAND -- signal ----------------- The signal command will send a signal to the OpenVPN daemon. The signal can be one of SIGHUP, SIGTERM, SIGUSR1, or SIGUSR2. Command example: signal SIGUSR1 -- send a SIGUSR1 signal to daemon COMMAND -- state ---------------- Show the current OpenVPN state, show state history, or enable real-time notification of state changes. These are the OpenVPN states: CONNECTING -- OpenVPN's initial state. WAIT -- (Client only) Waiting for initial response from server. AUTH -- (Client only) Authenticating with server. GET_CONFIG -- (Client only) Downloading configuration options from server. ASSIGN_IP -- Assigning IP address to virtual network interface. ADD_ROUTES -- Adding routes to system. CONNECTED -- Initialization Sequence Completed. RECONNECTING -- A restart has occurred. EXITING -- A graceful exit is in progress. RESOLVE -- (Client only) DNS lookup TCP_CONNECT -- (Client only) Connecting to TCP server AUTH_PENDING -- (Client only) Authentication pending Command examples: state -- Print current OpenVPN state. state on -- Enable real-time notification of state changes. state off -- Disable real-time notification of state changes. state all -- Print current state history. state 3 -- Print the 3 most recent state transitions. state on all -- Atomically show state history while at the same time enable real-time state notification of future state transitions. The output format consists of up to 9 comma-separated parameters: (a) the integer unix date/time, (b) the state name, (c) optional descriptive string (used mostly on RECONNECTING and EXITING to show the reason for the disconnect), (d) optional TUN/TAP local IPv4 address (e) optional address of remote server, (f) optional port of remote server, (g) optional local address, (h) optional local port, and (i) optional TUN/TAP local IPv6 address. Fields (e)-(h) are shown for CONNECTED state, (d) and (i) are shown for ASSIGN_IP and CONNECTED states. (e) is available starting from OpenVPN 2.1 (f)-(i) are available starting from OpenVPN 2.4 For AUTH_PENDING, if (c) is present, it would read as "timeout number" where number is the number of seconds before authentication will timeout. It is printed as an unsigned integer (%u). Real-time state notifications will have a ">STATE:" prefix prepended to them. COMMAND -- status ----------------- Show current daemon status information, in the same format as that produced by the OpenVPN --status directive. Command examples: status -- Show status information using the default status format version. status 3 -- Show status information using the format of --status-version 3. COMMAND -- username ------------------- See the "password" section above. COMMAND -- verb --------------- Change the OpenVPN --verb parameter. The verb parameter controls the output verbosity, and may range from 0 (no output) to 15 (maximum output). See the OpenVPN man page for additional info on verbosity levels. Command examples: verb 4 -- change the verb parameter to 4 verb -- show the current verb setting COMMAND -- version ------------------ Set the version (integer) of Management Interface supported by the client or show the current OpenVPN and Management Interface versions. Command examples: version 2 -- Change management version of client to 2 (default = 1) version -- Show the version of OpenVPN and its Management Interface COMMAND -- auth-retry --------------------- Set the --auth-retry setting to control how OpenVPN responds to username/password authentication errors. See the manual page for more info. Command examples: auth-retry interact -- Don't exit when bad username/passwords are entered. Query for new input and retry. COMMAND -- needok (OpenVPN 2.1 or higher) ------------------------------------------ Confirm a ">NEED-OK" real-time notification, normally used by OpenVPN to block while waiting for a specific user action. Example: OpenVPN needs the user to insert a cryptographic token, so it sends a real-time notification: >NEED-OK:Need 'token-insertion-request' confirmation MSG:Please insert your cryptographic token The management interface client, if it is a GUI, can flash a dialog box containing the text after the "MSG:" marker to the user. When the user acknowledges the dialog box, the management interface client should issue either: needok token-insertion-request ok or needok token-insertion-request cancel COMMAND -- needstr (OpenVPN 2.1 or higher) ------------------------------------------- Confirm a ">NEED-STR" real-time notification, normally used by OpenVPN to block while waiting for a specific user input. Example: OpenVPN needs the user to specify some input, so it sends a real-time notification: >NEED-STR:Need 'name' input MSG:Please specify your name The management interface client, if it is a GUI, can flash a dialog box containing the text after the "MSG:" marker to the user. When the user acknowledges the dialog box, the management interface client should issue this command: needstr name "John" COMMAND -- pkcs11-id-count (OpenVPN 2.1 or higher) --------------------------------------------------- Retrieve available number of certificates. Example: pkcs11-id-count >PKCS11ID-COUNT:5 COMMAND -- pkcs11-id-get (OpenVPN 2.1 or higher) ------------------------------------------------- Retrieve certificate by index, the ID string should be provided as PKCS#11 identity, the blob is a base 64 encoded certificate. Example: pkcs11-id-get 1 PKCS11ID-ENTRY:'1', ID:'', BLOB:'' COMMAND -- client-auth (OpenVPN 2.1 or higher) ----------------------------------------------- Authorize a ">CLIENT:CONNECT" or ">CLIENT:REAUTH" request and specify "client-connect" configuration directives in a subsequent text block. The OpenVPN server should have been started with the --management-client-auth directive so that it will ask the management interface to approve client connections. client-auth {CID} {KID} line_1 line_2 ... line_n END CID,KID -- client ID and Key ID. See documentation for ">CLIENT:" notification for more info. line_1 to line_n -- client-connect configuration text block, as would be returned by a --client-connect script. The text block may be null, with "END" immediately following the "client-auth" line (using a null text block is equivalent to using the client-auth-nt command). A client-connect configuration text block contains OpenVPN directives that will be applied to the client instance object representing a newly connected client. COMMAND -- client-auth-nt (OpenVPN 2.1 or higher) -------------------------------------------------- Authorize a ">CLIENT:CONNECT" or ">CLIENT:REAUTH" request without specifying client-connect configuration text. The OpenVPN server should have been started with the --management-client-auth directive so that it will ask the management interface to approve client connections. client-auth-nt {CID} {KID} CID,KID -- client ID and Key ID. See documentation for ">CLIENT:" notification for more info. COMMAND -- client-pending-auth (OpenVPN 2.5 or higher) ---------------------------------------------------- Instruct OpenVPN server to send AUTH_PENDING and INFO_PRE message to signal a pending authenticating to the client. A pending auth means that the connecting requires extra authentication like a one time password or doing a single sign on via web. client-pending-auth {CID} {EXTRA} {TIMEOUT} The server will send AUTH_PENDING and INFO_PRE,{EXTRA} to the client. If the client supports accepting keywords to AUTH_PENDING (announced via IV_PROTO), TIMEOUT parameter will be also be announced to the client to allow it to modify its own timeout. The client is expected to inform the user that authentication is pending and display the extra information and also show the user the remaining time to complete the auth if applicable. Receiving an AUTH_PENDING message will make the client change its timeout to the timeout proposed by the server, even if the timeout is shorter. If the client does not receive a packet from the server for hand-window the connection times out regardless of the timeout. This ensures that the connection still times out relatively quickly in case of network problems. The client will continuously send PULL_REQUEST messages to the server until the timeout is reached. This message also triggers an ACK message from the server that resets the hand-window based timeout. Both client and server limit the maximum timeout to the smaller value of half the --tls-reneg minimum time and --hand-window time (defaults to 60s). For the format of {EXTRA} see below. For OpenVPN server this is a stateless operation and needs to be followed by a client-deny/client-auth[-nt] command (that is the result of the out of band authentication). Before issuing a client-pending-auth to a client instead of a client-auth/client-deny, the server should check the IV_SSO environment variable for whether the method is supported. Currently defined methods are crtext for challenge/response using text (e.g., TOTP), openurl and proxy_url for opening a URL in the client to continue authentication. A client supporting the first two methods would set setenv IV_SSO openurl,crtext The variable name IV_SSO is historic as AUTH_PENDING was first used to signal single sign on support. To keep compatibility with existing implementations the name IV_SSO is kept in lieu of a better name. The management interface of the client receives notification of pending auth via >STATE:datetime,AUTH_PENDING,[timeout number] If {EXTRA} is present the client is informed using INFOMSG notification as >INFOMSG:{EXTRA} where {EXTRA} is formatted as received from the server. Currently defined formats for {EXTRA} are detailed below. openurl ======== For a web based extra authentication (like for SSO/SAML) {EXTRA} should be OPEN_URL:url and client should ask the user to open the URL to continue. The space in a control message is limited, so this url should be kept short to avoid issues. If a longer url is required a URL that redirects to the longer URL should be sent instead. A complete documentation how URLs should be handled on the client is available in the openvpn3 repository: https://github.com/OpenVPN/openvpn3/blob/master/doc/webauth.md proxy_url ======== This is a variant of openurl that allows opening a url via an HTTP proxy. It could be used to avoid issues with OpenVPN connection's persist-tun that may cause the web server to be unreachable. The client should announce proxy_url in its IV_SSO and parse the PROXY_URL message. The format of {EXTRA} in this case is PROXY_URL:::::url The proxy should be a literal IPv4 address or IPv6 address enclosed in [] to avoid ambiguity in parsing. A literal IP address is preferred as DNS might not be available when the client needs to open the url. The IP address will usually be the address that client uses to connect to the VPN server. For dual-homed VPN servers, the server should respond with the same address that the client connects to. This address is also usually excluded from being redirected over the VPN by a host route. If the platform (like Android) uses another way of protecting the VPN connection from routing loops, the client needs to also exclude the connection to the proxy in the same manner. Should another IP be used, then the VPN configuration should include a route statement to exclude that address from being routed over the VPN. crtext ======= The format of {EXTRA} is similar to the already used two step authentication described in Challenge/Response Protocol section of this document. Since most of the fields are not necessary or can be inferred, only the and fields are used: CR_TEXT:: : a series of optional, comma-separated flags: E : echo the response when the user types it. R : a response is required. : the challenge text to be shown to the user. The client should return the response to the crtext challenge using the cr-response command. COMMAND -- client-deny (OpenVPN 2.1 or higher) ----------------------------------------------- Deny a ">CLIENT:CONNECT" or ">CLIENT:REAUTH" request. client-deny {CID} {KID} "reason-text" ["client-reason-text"] CID,KID -- client ID and Key ID. See documentation for ">CLIENT:" notification for more info. reason-text: a human-readable message explaining why the authentication request was denied. This message will be output to the OpenVPN log file or syslog. client-reason-text: a message that will be sent to the client as part of the AUTH_FAILED message. Note that client-deny denies a specific Key ID (pertaining to a TLS renegotiation). A client-deny command issued in response to an initial TLS key negotiation (notified by ">CLIENT:CONNECT") will terminate the client session after returning "AUTH-FAILED" to the client. On the other hand, a client-deny command issued in response to a TLS renegotiation (">CLIENT:REAUTH") will invalidate the renegotiated key, however the TLS session associated with the currently active key will continue to live for up to --tran-window seconds before expiration. To immediately kill a client session, use "client-kill". COMMAND -- client-kill (OpenVPN 2.1 or higher) ----------------------------------------------- Immediately kill a client instance by CID. client-kill {CID} CID -- client ID. See documentation for ">CLIENT:" notification for more info. COMMAND -- client-pf (OpenVPN 2.1 or higher) --------------------------------------------- Push a packet filter file to a specific client. The OpenVPN server should have been started with the --management-client-pf directive so that it will require that VPN tunnel packets sent or received by client instances must conform to that client's packet filter configuration. client-pf {CID} line_1 line_2 ... line_n END CID -- client ID. See documentation for ">CLIENT:" notification for more info. line_1 to line_n -- the packet filter configuration file for this client. Packet filter file grammar: [CLIENTS DROP|ACCEPT] {+|-}common_name1 {+|-}common_name2 . . . [SUBNETS DROP|ACCEPT] {+|-}subnet1 {+|-}subnet2 . . . [END] Subnet: IP-ADDRESS | IP-ADDRESS/NUM_NETWORK_BITS | "unknown" CLIENTS refers to the set of clients (by their common-name) which this instance is allowed ('+') to connect to, or is excluded ('-') from connecting to. Note that in the case of client-to-client connections, such communication must be allowed by the packet filter configuration files of both clients AND the --client-to-client directive must have been specified in the OpenVPN server config. SUBNETS refers to IP addresses or IP address subnets which this client instance may connect to ('+') or is excluded ('-') from connecting to, and applies to IPv4 and ARP packets. The special "unknown" tag refers to packets of unknown type, i.e. a packet that is not IPv4 or ARP. DROP or ACCEPT defines default policy when there is no explicit match for a common-name or subnet. The [END] tag must exist. Notes: * The SUBNETS section currently only supports IPv4 addresses and subnets. * A given client or subnet rule applies to both incoming and outgoing packets. * The CLIENTS list is order-invariant. Because the list is stored as a hash-table, the order of the list does not affect its function. * The SUBNETS table is scanned sequentially, and the first item to match is chosen. Therefore the SUBNETS table is NOT order-invariant. * No client-to-client communication is allowed unless the --client-to-client configuration directive is enabled AND the CLIENTS list of BOTH clients allows the communication. Example packet filter spec, as transmitted to the management interface: client-pf 42 [CLIENTS ACCEPT] -accounting -enigma [SUBNETS DROP] -10.46.79.9 +10.0.0.0/8 [END] END The above example sets the packet filter policy for the client identified by CID=42. This client may connect to all other clients except those having a common name of "accounting" or "enigma". The client may only interact with external IP addresses in the 10.0.0.0/8 subnet, however access to 10.46.79.9 is specifically excluded. Another example packet filter spec, as transmitted to the management interface: client-pf 99 [CLIENTS DENY] +public [SUBNETS ACCEPT] +10.10.0.1 -10.0.0.0/8 -unknown [END] END The above example sets the packet filter policy for the client identified by CID=99. This client may not connect to any other clients except those having a common name of "public". It may interact with any external IP address except those in the 10.0.0.0/8 netblock. However interaction with one address in the 10.0.0.0/8 netblock is allowed: 10.10.0.1. Also, the client may not interact with external IP addresses using an "unknown" protocol (i.e. one that is not IPv4 or ARP). COMMAND -- remote (OpenVPN AS 2.1.5/OpenVPN 2.3 or higher) -------------------------------------------- Provide remote host/port in response to a >REMOTE notification (client only). Requires that the --management-query-remote directive is used. remote ACTION [HOST PORT] The "remote" command should only be given in response to a >REMOTE notification. For example, the following >REMOTE notification indicates that the client config file would ordinarily connect to vpn.example.com port 1194 (UDP): >REMOTE:vpn.example.com,1194,udp Now, suppose we want to override the host and port, connecting instead to vpn.otherexample.com port 1234. After receiving the above notification, use this command: remote MOD vpn.otherexample.com 1234 To accept the same host and port as the client would ordinarily have connected to, use this command: remote ACCEPT To skip the current connection entry and advance to the next one, use this command: remote SKIP COMMAND -- proxy (OpenVPN 2.3 or higher) -------------------------------------------- Provide proxy server host/port and flags in response to a >PROXY notification (client only). Requires that the --management-query-proxy directive is used. proxy TYPE HOST PORT ["nct"] The "proxy" command must only be given in response to a >PROXY notification. Use the "nct" flag if you only want to allow non-cleartext auth with the proxy server. The following >PROXY notification indicates that the client config file would ordinarily connect to the first --remote configured, vpn.example.com using TCP: >PROXY:1,TCP,vpn.example.com Now, suppose we want to connect to the remote host using the proxy server proxy.intranet port 8080 with secure authentication only, if required. After receiving the above notification, use this command: proxy HTTP proxy.intranet 8080 nct You can also use the SOCKS keyword to pass a SOCKS server address, like: proxy SOCKS fe00::1 1080 To accept connecting to the host and port directly, use this command: proxy NONE COMMAND -- cr-response (OpenVPN 2.5 or higher) ------------------------------------------------- Provides support for sending responses to a challenge/response query via INFOMSG,CR_TEXT (client-only). The response should be base64 encoded: cr-response SGFsbG8gV2VsdCE= This command is intended to be used after the client receives a CR_TEXT challenge (see client-pending-auth section). The argument to cr-response is the base64 encoded answer to the challenge and depends on the challenge itself. For a TOTP challenge this would be a number encoded as base64; for a challenge like "what day is it today?" it would be a string encoded as base64. COMMAND -- pk-sig (OpenVPN 2.5 or higher, management version > 1) COMMAND -- rsa-sig (OpenVPN 2.3 or higher, management version <= 1) ----------------------------------------------------------------- Provides support for external storage of the private key. Requires the --management-external-key option. This option can be used instead of "key" in client mode, and allows the client to run without the need to load the actual private key. When the SSL protocol needs to perform a sign operation, the data to be signed will be sent to the management interface via a notification as follows: >PK_SIGN:[BASE64_DATA],[ALG] (if client announces support for management version > 2) >PK_SIGN:[BASE64_DATA] (if client announces support for management version > 1) >RSA_SIGN:[BASE64_DATA] (only older clients will be prompted like this) The management interface client should then create an appropriate signature of the (decoded) BASE64_DATA using the private key and return the SSL signature as follows: pk-sig (or rsa-sig) [BASE64_SIG_LINE] . . . END Base 64 encoded output of RSA_private_encrypt for RSA or ECDSA_sign() for EC using OpenSSL or mbedtls_pk_sign() using mbed TLS will provide a correct signature. The rsa-sig interface expects PKCS1 padded signatures for RSA keys (RSA_PKCS1_PADDING). EC signatures are always unpadded. This capability is intended to allow the use of arbitrary cryptographic service providers with OpenVPN via the management interface. New and updated clients are expected to use the version command to announce a version > 1 and handle '>PK_SIGN' prompt and respond with 'pk-sig'. The signature algorithm is indicated in the PK_SIGN request only if the management client-version is > 2. In particular, to support TLS1.3 and TLS1.2 using OpenSSL 1.1.1, unpadded signature support is required and this can be indicated in the signing request only if the client version is > 2" The currently defined padding algorithms are: - RSA_PKCS1_PADDING - PKCS1 padding and RSA signature - RSA_NO_PADDING - No padding may be added for the signature - ECDSA - EC signature. COMMAND -- certificate (OpenVPN 2.4 or higher) ---------------------------------------------- Provides support for external storage of the certificate. Requires the --management-external-cert option. This option can be used instead of "cert" in client mode. On SSL protocol initialization a notification will be sent to the management interface with a hint as follows: >NEED-CERTIFICATE:macosx-keychain:subject:o=OpenVPN-TEST The management interface client should use the hint to obtain the specific SSL certificate and then return base 64 encoded certificate as follows: certificate [BASE64_CERT_LINE] . . . END This capability is intended to allow the use of certificates stored outside of the filesystem (e.g. in Mac OS X Keychain) with OpenVPN via the management interface. OUTPUT FORMAT ------------- (1) Command success/failure indicated by "SUCCESS: [text]" or "ERROR: [text]". (2) For commands which print multiple lines of output, the last line will be "END". (3) Real-time messages will be in the form ">[source]:[text]", where source is "CLIENT", "ECHO", "FATAL", "HOLD", "INFO", "LOG", "NEED-OK", "PASSWORD", or "STATE". REAL-TIME MESSAGE FORMAT ------------------------ The OpenVPN management interface produces two kinds of output: (a) output from a command, or (b) asynchronous, real-time output which can be generated at any time. Real-time messages start with a '>' character in the first column and are immediately followed by a type keyword indicating the type of real-time message. The following types are currently defined: BYTECOUNT -- Real-time bandwidth usage notification, as enabled by "bytecount" command when OpenVPN is running as a client. BYTECOUNT_CLI -- Real-time bandwidth usage notification per-client, as enabled by "bytecount" command when OpenVPN is running as a server. CLIENT -- Notification of client connections and disconnections on an OpenVPN server. Enabled when OpenVPN is started with the --management-client-auth option. CLIENT notifications may be multi-line. See "The CLIENT notification" section below for detailed info. ECHO -- Echo messages as controlled by the "echo" command. FATAL -- A fatal error which is output to the log file just prior to OpenVPN exiting. HOLD -- Used to indicate that OpenVPN is in a holding state and will not start until it receives a "hold release" command. INFO -- Informational messages such as the welcome message. LOG -- Log message output as controlled by the "log" command. NEED-OK -- OpenVPN needs the end user to do something, such as insert a cryptographic token. The "needok" command can be used to tell OpenVPN to continue. NEED-STR -- OpenVPN needs information from end, such as a certificate to use. The "needstr" command can be used to tell OpenVPN to continue. PASSWORD -- Used to tell the management interface client that OpenVPN needs a password, also to indicate password verification failure. STATE -- Shows the current OpenVPN state, as controlled by the "state" command. INFOMSG -- Authentication related info from server such as CR_TEXT or OPEN_URL. See description under client-pending-auth The CLIENT notification ----------------------- The ">CLIENT:" notification is enabled by the --management-client-auth OpenVPN configuration directive that gives the management interface client the responsibility to authenticate OpenVPN clients after their client certificate has been verified. CLIENT notifications may be multi-line, and the sequentiality of a given CLIENT notification, its associated environmental variables, and the terminating ">CLIENT:ENV,END" line are guaranteed to be atomic. CLIENT notification types: (1) Notify new client connection ("CONNECT") or existing client TLS session renegotiation ("REAUTH"). Information about the client is provided by a list of environmental variables which are documented in the OpenVPN man page. The environmental variables passed are equivalent to those that would be passed to an --auth-user-pass-verify script. >CLIENT:CONNECT|REAUTH,{CID},{KID} >CLIENT:ENV,name1=val1 >CLIENT:ENV,name2=val2 >CLIENT:ENV,... >CLIENT:ENV,END (2) Notify successful client authentication and session initiation. Called after CONNECT. >CLIENT:ESTABLISHED,{CID} >CLIENT:ENV,name1=val1 >CLIENT:ENV,name2=val2 >CLIENT:ENV,... >CLIENT:ENV,END (3) Notify existing client disconnection. The environmental variables passed are equivalent to those that would be passed to a --client-disconnect script. >CLIENT:DISCONNECT,{CID} >CLIENT:ENV,name1=val1 >CLIENT:ENV,name2=val2 >CLIENT:ENV,... >CLIENT:ENV,END (4) Notify that a particular virtual address or subnet is now associated with a specific client. >CLIENT:ADDRESS,{CID},{ADDR},{PRI} (5) Text based challenge/Response >CLIENT:CR_RESPONSE,{CID},{KID},{response_base64} >CLIENT:ENV,name1=val1 >CLIENT:ENV,name2=val2 >CLIENT:ENV,... >CLIENT:ENV,END Use of the cr-response command on the client side will trigger this message on the server side. CR_RESPONSE notification fulfills the same purpose as the CRV1 response in the traditional challenge/response. See that section below for more details. Since this uses the same cid as in the original client-pending-auth challenge, we do not include the username and opaque session data in this notification. The string {response_base64} only contains the actual response received from the client. It is important to note that OpenVPN2 merely passes the authentication information and does not do any further checks. (E.g. if a CR was issued before or if multiple CR responses were sent from the client or if data has a valid base64 encoding) This interface should be be sufficient for almost all challenge/response system that can be implemented with a single round and base64 encoding of the response. Mechanisms that need multiple rounds or more complex answers should implement a different response type than CR_RESPONSE. Variables: CID -- Client ID, numerical ID for each connecting client, sequence = 0,1,2,... KID -- Key ID, numerical ID for the key associated with a given client TLS session, sequence = 0,1,2,... PRI -- Primary (1) or Secondary (0) VPN address/subnet. All clients have at least one primary IP address. Secondary address/subnets are associated with client-specific "iroute" directives. ADDR -- IPv4 address/subnet in the form 1.2.3.4 or 1.2.3.0/255.255.255.0 In the unlikely scenario of an extremely long-running OpenVPN server, CID and KID should be assumed to recycle to 0 after (2^32)-1, however this recycling behavior is guaranteed to be collision-free. Command Parsing --------------- The management interface uses the same command line lexical analyzer as is used by the OpenVPN config file parser. Whitespace is a parameter separator. Double quotation or single quotation characters ("", '') can be used to enclose parameters containing whitespace. Backslash-based shell escaping is performed, using the following mappings, when not in single quotations: \\ Maps to a single backslash character (\). \" Pass a literal doublequote character ("), don't interpret it as enclosing a parameter. \[SPACE] Pass a literal space or tab character, don't interpret it as a parameter delimiter. Challenge/Response Protocol --------------------------- The OpenVPN Challenge/Response Protocol allows an OpenVPN server to generate challenge questions that are shown to the user, and to see the user's responses to those challenges. Based on the responses, the server can allow or deny access. The protocol can be used to implement multi-factor authentication because the user must enter an additional piece of information, in addition to a username and password, to successfully authenticate. In multi-factor authentication, this information is used to prove that the user possesses a certain key-like device such as cryptographic token or a particular mobile phone. Two variations on the challenge/response protocol are supported: the "static" and "dynamic" protocols: * The static protocol uses OpenVPN's "--static-challenge" option. * The dynamic protocol does not involve special OpenVPN options or actions. It is an agreement between the auth-user-pass verification process on the server and the management interface client to use custom strings that begin with "['CRV1" in "Verification Failed" messages. (The "[" character and a matching "]" character at the end of the message are added by the client OpenVPN program, and are not present in the string generated by the auth-user-pass verification process or in the string sent by the server.) Dynamic protocol: The OpenVPN dynamic challenge/response protocol works by returning a specially formatted error message after initial successful authentication. The error message has two purposes: 1. It causes OpenVPN to restart the connection attempt. 2. It contains information about the challenge, which should be used to construct the response to the next authentication request (which will occur after the restart). Notes: * '--auth-retry interact' must be in effect so that the connection is restarted and credentials are requested again. * '--auth-retry none' (which is the default) will cause OpenVPN to exit with a fatal error without retrying and the dynamic challenge/response will never happen because "Need 'Auth' username/password" will not be sent. The error message is formatted as follows: >PASSWORD:Verification Failed: 'Auth' ['CRV1::::'] : a series of optional, comma-separated flags: E : echo the response when the user types it. R : a response is required. : an opaque string that should be returned to the server along with the response. : the username encoded as base 64. : the challenge text to be shown to the user. may not contain colon characters (":"), but may. Example challenge: CRV1:R,E:Om01u7Fh4LrGBS7uh0SWmzwabUiGiW6l:Y3Ix:Please enter token PIN The next time the username and password are requested with >PASSWORD:Need 'Auth' username/password the management interface client should display the challenge text and, if the R flag is specified, get a response from the user. The management interface client should respond: username "Auth" password "Auth" CRV1:::: Where is the username decoded from , is taken from the challenge request, and is what the user entered in response to the challenge, which can be an empty string. If the R flag is not present, should be an empty string. (As in all username/password responses described in the "COMMAND -- password and username" section above, the username and/or password can be in quotes, and special characters such as double quotes or backslashes must be escaped. See the "Command Parsing" section above for more info.) Example response (suppose the user enters "8675309" for the token PIN): username "Auth" cr1 password "Auth" CRV1::Om01u7Fh4LrGBS7uh0SWmzwabUiGiW6l::8675309 ("Y3Ix" is the base 64 encoding of "cr1".) Static protocol: The static protocol differs from the dynamic protocol in that the challenge question is sent to the management interface client in a a username/password request, and the username, password, and response are delivered back to the server in response to that request. OpenVPN's --static-challenge option is used to provide the challenge text to OpenVPN and indicate whether or not the response should be echoed. When credentials are needed and the --static-challenge option is used, the management interface will send: >PASSWORD:Need 'Auth' username/password SC:, ECHO: "1" if response should be echoed, "0" to not echo TEXT: challenge text that should be shown to the user to facilitate their response For example: >PASSWORD:Need 'Auth' username/password SC:1,Please enter token PIN The above notification indicates that OpenVPN needs a --auth-user-pass username and password plus a response to a static challenge ("Please enter token PIN"). The "1" after the "SC:" indicates that the response should be echoed. The management interface client in this case should add the static challenge text to the auth dialog followed by a field for the user to enter a response. Then the management interface client should pack the password and response together into an encoded password and send: username "Auth" password "Auth" "SCRV1::" Where is the username entered by the user, is the base 64 encoding of the password entered by the user, and is the base 64 encoding of the response entered by the user. The and/or the can be empty strings. (As in all username/password responses described in the "COMMAND -- password and username" section above, the username can be in quotes, and special characters such as double quotes or backslashes must be escaped. See the "Command Parsing" section above for more info.) For example, if user "foo" entered "bar" as the password and 8675309 as the PIN, the following management interface commands should be issued: username "Auth" foo password "Auth" "SCRV1:YmFy:ODY3NTMwOQ==" ("YmFy" is the base 64 encoding of "bar" and "ODY3NTMwOQ==" is the base 64 encoding of "8675309".)