ProFTPD module mod_exec



This module is contained in the mod_exec.c file for ProFTPD 1.3.x, found here, and is not compiled by default. Installation instructions are discussed here.

The mod_exec module can be used to execute external programs or scripts at various points in the process of handling FTP commands. By conscious design, the core ProFTPD engine does not and will not execute external programs. This is a security decision, as it was decided not to allow ProFTPD to serve as a means of compromising a system or disclosing information via bugs in external programs or scripts. Use of this module allows for such external programs to be executed, and also opens up the server to the mentioned possibilities of compromise or disclosure via those programs.

YOU HAVE BEEN WARNED
USE AT YOUR OWN RISK

Please read the usage section to know the other caveats with this module.

The most current version of mod_exec is distributed with the ProFTPD source code.

Author

Please contact TJ Saunders <tj at castaglia.org> with any questions, concerns, or suggestions regarding this module.

Directives


ExecBeforeCommand

Syntax: ExecBeforeCommand cmds path [arg1 arg2 ...]
Default: None
Context: "server config" <VirtualHost>, <Global>, <Anonymous>, <Directory>
Module: mod_exec
Compatibility: 1.2.8 and later

The ExecBeforeCommand directive is used to execute the program or script at path before the handling of any FTP command listed in cmds, where cmds is a comma-delimited list of FTP commands. The command groups of the <Limit> directive, such as READ, WRITE, and ALL, may also be used. The program will be executed with the privileges of the logged-in user.

Any number of arbitrary arguments may be configured to pass to the script. In addition, the "cookies" supported by the ExecEnviron directive may also be used in the script argument list.

Important: use of DefaultRoot will cause complications (to be elaborated upon soon).

Example:

  ExecBeforeCommand RETR /path/to/ftp-prep --file %f

See Also: ExecEnviron, ExecOnCommand, ExecOnConnect, ExecOnError, ExecOnExit, ExecOnRestart, <Limit>


ExecEngine

Syntax: ExecEngine on|off
Default: None
Context: "server config", <VirtualHost>, <Global>
Module: mod_exec
Compatibility: 1.2.5rc2 and later

The ExecEngine directive enables or disables the module's runtime exec engine. If it is set to off this module will not manipulate environment variables or execute external scripts. Use this directive to disable the module instead of commenting out all mod_exec directives.


ExecEnviron

Syntax: ExecEnviron key value
Default: None
Context: "server config", <VirtualHost>, <Global>
Module: mod_exec
Compatibility: 1.2.5rc2 and later

The ExecEnviron directive is used to set the environment variables in the environment created for the script to be executed. The current environment is not passed directly to the script; this is to prevent unwanted information leakage. The given key parameter will be uppercased, to follow the convention for environment variable keys.

The value parameter may be any arbitrary string which may contain any of the following "cookies", which will be substituted with the corresponding value before the script is executed:

The value parameter may be also be "-", which indicates that the current value of the environment variable of name key should be used (e.g. PATH). If there is no environment of name key when "-" is used, it will be created with a blank string as the value.


ExecLog

Syntax: ExecLog file|"none"
Default: None
Context: "server config", <VirtualHost>, <Global>
Module: mod_exec
Compatibility: 1.2.5rc2 and later

The ExecLog directive is used to specify a log file for mod_exec reporting and debugging, and can be done a per-server basis. The file parameter must be the full path to the file to use for logging. Note that this path must not be to a world-writeable directory and, unless AllowLogSymlinks is explicitly set to on (generally a bad idea), the path must not be a symbolic link.

If file is "none", no logging will be done at all; this setting can be used to override an ExecLog setting inherited from a <Global> context.


ExecOnCommand

Syntax: ExecOnCommand cmds path [arg1 arg2 ...]
Default: None
Context: "server config" <VirtualHost>, <Global>, <Anonymous>, <Directory>
Module: mod_exec
Compatibility: 1.2.5rc2 and later

The ExecOnCommand directive is used to execute the program or script at path after the successful completion of any FTP command listed in cmds, where cmds is a comma-delimited list of FTP commands. The command groups of the <Limit> directive, such as READ, WRITE, and ALL, may also be used. The program will be executed with the privileges of the logged-in user.

Any number of arbitrary arguments may be configured to pass to the script. In addition, the "cookies" supported by the ExecEnviron directive may also be used in the script argument list.

Important: use of DefaultRoot will cause complications (to be elaborated upon soon).

Example:

  ExecOnCommand APPE,STOR /path/to/ftp-email-script --user %u --file %f

See Also: ExecBeforeCommand, ExecEnviron, ExecOnConnect, ExecOnError, ExecOnExit, ExecOnRestart, <Limit>


ExecOnConnect

Syntax: ExecOnConnect path [arg1 arg2 ...]
Default: None
Context: "server config" <VirtualHost>, <Global>, <Anonymous>, <Directory>
Module: mod_exec
Compatibility: 1.2.5rc2 and later

The ExecOnConnect directive is used to execute the program or script at path whenever a client connects to the server. The program will be executed with the privileges of the contacted server, which are set via the User/Group directives.

Any number of arbitrary arguments may be configured to pass to the script. In addition, the "cookies" supported by the ExecEnviron directive may also be used in the script argument list.

Example:

  ExecOnConnect /path/to/ftp-logger --ip %a --dns %h

See Also: ExecBeforeCommand, ExecEnviron, ExecOnCommand, ExecOnError, ExecOnExit, ExecOnRestart


ExecOnError

Syntax: ExecOnError cmds path [arg1 arg2 ...]
Default: None
Context: "server config" <VirtualHost>, <Global>, <Anonymous>, <Directory>
Module: mod_exec
Compatibility: 1.2.5rc2 and later

The ExecOnError directive is used to execute the program or script at path if an error occurs while processing any FTP command listed in cmds, where cmds is a comma-delimited list of FTP commands. The command groups of the <Limit> directive, such as READ, WRITE, and ALL, may also be used. The program will be executed with the privileges of the logged-in user.

Any number of arbitrary arguments may be configured to pass to the script. In addition, the "cookies" supported by the ExecEnviron directive may also be used in the script argument list.

Important: use of DefaultRoot will cause complications (to be elaborated upon soon).

Example:

  ExecOnError APPE,STOR /path/to/ftp-cleanup-script --user %u --file %f
See Also: ExecBeforeCommand, ExecEnviron, ExecOnCommand, ExecOnConnect, ExecOnExit, ExecOnRestart, <Limit>


ExecOnEvent

Syntax: ExecOnEvent event[*|~] path [arg1 arg2 ...]
Default: None
Context: "server config" <VirtualHost>, <Global>
Module: mod_exec
Compatibility: 1.2.10rc1 and later

The ExecOnEvent directive is used to execute the program or script at path when the given event occurs. The program will be executed with the privileges of the server (set via the User and Group directives in the proftpd.conffile), unless the event name is followed either by a "*" or a "~" character.

If the event name is followed by a "*", the program will be executed with root privileges. Note: this feature should be used very carefully. It allows scripts to modify things like firewall rules, but should be used only for such sensitive tasks.

If, on the other hand, the eevent name is followed by a "~", the program will be executed with the privileges of the logged-in user. Note: support for this feature first appeared in proftpd-1.3.5rc4.

Any number of arbitrary arguments may be configured to pass to the script. In addition, the "cookies" supported by the ExecEnviron directive may also be used in the script argument list.

Presently only two specific events are supported: MaxConnectionRate and MaxInstances. These events happen when ever the limit configured by these configuration directives is reached.

This directive may be used several times to configure multiple programs to be invoked when event occurs.

Important: use of DefaultRoot will cause complications (to be elaborated upon soon).

Example:

  ExecOnEvent MaxConnectionRate* /path/to/ftp-firewall-script --ip %a
See Also: ExecBeforeCommand, ExecEnviron, ExecOnCommand, ExecOnConnect, ExecOnExit, ExecOnRestart


ExecOnExit

Syntax: ExecOnExit path [arg1 arg2 ...]
Default: None
Context: "server config" <VirtualHost>, <Global>, <Anonymous>, <Directory>
Module: mod_exec
Compatibility: 1.2.8 and later

The ExecOnExit directive is used to execute the program or script at path whenever a client disconnects to the server. The program will be executed with the privileges of the contacted server, which are set via the User/Group directives.

Any number of arbitrary arguments may be configured to pass to the script. In addition, the "cookies" supported by the ExecEnviron directive may also be used in the script argument list.

Example:

  ExecOnExit /path/to/ftp-logger --ip %a --dns %h

See Also: ExecBeforeCommand, ExecEnviron, ExecOnCommand, ExecOnConnect, ExecOnError, ExecOnRestart


ExecOnRestart

Syntax: ExecOnRestart path [arg1 arg2 ...]
Default: None
Context: "server config" <VirtualHost>, <Global>, <Anonymous>, <Directory>
Module: mod_exec
Compatibility: 1.2.5rc2 and later

The ExecOnRestart directive is used to execute the program or script at path whenever the server receives a SIGHUP signal. The program will be executed with the privileges of the contacted server, which are set via the User/Group directives.

Any number of arbitrary arguments may be configured to pass to the script. In addition, the "cookies" supported by the ExecEnviron directive may also be used in the script argument list.

Example:

  ExecOnRestart /path/to/ftp-counter-reset
See Also: ExecBeforeCommand, ExecEnviron, ExecOnCommand, ExecOnConnect, ExecOnError, ExecOnExit


ExecOptions

Syntax: ExecOptions opt1 ...
Default: None
Context: "server config" <VirtualHost>, <Global>
Module: mod_exec
Compatibility: 1.2.9rc2 and later

The ExecOptions directive is used to configure various optional behavior of mod_exec.

Example:

  ExecOptions logStderr sendStdout

The currently implemented options are:


ExecTimeout

Syntax: ExecTimeout seconds
Default: None
Context: "server config" <VirtualHost>, <Global>
Module: mod_exec
Compatibility: 1.2.9rc2 and later

The ExecTimeout directive is used to set a limit on how long the executed commands can run. Processes that exceed the configured timeout will first be sent SIGTERM, to allow them to cleanly shutdown. If the process is still around, it will then be sent SIGKILL, which cannot be ignored. A value of zero configures an infinite timeout (not recommended).


Usage

Example configuration:
  <IfModule mod_exec.c>
    ExecEngine on
    ExecLog /var/log/ftpd/exec.log
    ExecOnConnect /path/to/script
  </IfModule>

This module will not work properly for <Anonymous> logins, or for logins that are affected by DefaultRoot. These directives use the chroot(2) system call, which wreaks havoc when it comes to scripts. The path to script/shell interpreters often assume a certain location that is no longer valid within a chroot. In addition, most modern operating systems use dynamically loaded libraries (.so libraries) for many binaries, including script/shell interpreters. The location of these libraries, when they come to be loaded, are also assumed; those assumptions break within a chroot. Perl, in particular, is so wrought with filesystem location assumptions that it's almost impossible to get a Perl script to work within a chroot, short of installing Perl itself into the chroot environment.

In short, this module is probably not what you want. And, try as I might, I cannot convince users that this module is not what they want. Therefore, I'll let you try to use this module yourself, and you can prove to yourself that it probably won't do what you want.

As an alternative to mod_exec for executing arbitrary scripts/commands based on FTP command issued, file uploaded/downloaded, etc, I recommend using a logging FIFO-based approach, similar to what is illustrated here. This approach allows for any script you wish, and is not subject to the restrictions of a chroot, meaning that you can use DefaultRoot and still have arbitrary scripts executed. If requested, I can provide help in writing a FIFO reader to execute the necessary scripts.


Installation

To install mod_exec, copy the mod_exec.c file into
  proftpd-dir/contrib/
after unpacking the latest proftpd-1.3.x source code. Then follow the usual steps for using third-party modules in proftpd:
  ./configure --with-modules=mod_exec
To build mod_exec as a DSO module:
  ./configure --enable-dso --with-shared=mod_exec
Then follow the usual steps:
  make
  make install

Alternatively, if your proftpd was compiled with DSO support, you can use the prxs tool to build mod_exec as a shared module:

  prxs -c -i -d mod_exec.c

Frequently Asked Questions
Question: Why do %U/%u not work properly with ExecOnConnect?
Answer: Both %U and %u will be empty on ExecOnConnect because, at that point, the client has done a TCP connect to the server, but has not sent any sort of information (including user name). Which means that mod_exec does not have a user name to use at connect time.

One way to work around this limitation is to use a different trigger, e.g.:

  ExecOnCommand PASS ...
By the time the client sends the USER and PASS commands, the server will have the necessary user information to populate the %U/%u variables.



Author: $Author: castaglia $
Last Updated: $Date: 2014/01/21 22:39:11 $


© Copyright 2000-2014 TJ Saunders
All Rights Reserved