Summary
MultiTail's execute-on-match feature can incorporate attacker-controlled log content into a shell command with incomplete escaping. If an attacker can influence monitored input, they may execute commands with the privileges of the user running MultiTail.
MultiTail's execute-on-match feature can incorporate attacker-controlled log content into a shell command with incomplete escaping. If an attacker can influence monitored input, they may execute commands with the privileges of the user running MultiTail.
Affected context
The vulnerability occurs in MultiTail versions 7.1.5 and earlier when the -ex or -eX execute-on-match options are used to run a configured command after matching monitored input. Risk depends on whether an attacker can influence the contents of the monitored logs and whether the resulting input reaches the command execution path.
The vulnerability occurs in MultiTail versions 7.1.5 and earlier when the -ex or -eX execute-on-match options are used to run a configured command after matching monitored input. Risk depends on whether an attacker can influence the contents of the monitored logs and whether the resulting input reaches the command execution path.
Exploit preconditions
- Attack surface: MultiTail's
-exor-eXexecute-on-match functionality - Required access: Ability to influence data written to a monitored log or other input source
- Trigger point: A matching log entry causes the configured command to be constructed and executed
- Why exploitation is possible: Partial escaping leaves shell-interpreted metacharacters, including command substitution, active when the command is passed to
sh -c
- Attack surface: MultiTail's
-exor-eXexecute-on-match functionality - Required access: Ability to influence data written to a monitored log or other input source
- Trigger point: A matching log entry causes the configured command to be constructed and executed
- Why exploitation is possible: Partial escaping leaves shell-interpreted metacharacters, including command substitution, active when the command is passed to
sh -c
Why this happens
The underlying bug is unsafe construction of a shell command from attacker-controlled matched text. Although the input is placed inside double quotes and partially escaped, the escaping does not neutralize all shell syntax, allowing the shell to interpret embedded command-substitution expressions. Passing the resulting string to sh -c maps this behavior to CWE-78: Improper Neutralization of Special Elements used in an OS Command.
The underlying bug is unsafe construction of a shell command from attacker-controlled matched text. Although the input is placed inside double quotes and partially escaped, the escaping does not neutralize all shell syntax, allowing the shell to interpret embedded command-substitution expressions. Passing the resulting string to sh -c maps this behavior to CWE-78: Improper Neutralization of Special Elements used in an OS Command.
Potential impact
- An attacker may execute arbitrary commands as the MultiTail process user
- The monitored host or container could be compromised
- Confidential log data could be accessed or modified
- Credentials, tokens, or other process-accessible secrets could be exposed
- The process could be used for further lateral movement, depending on its privileges
- An attacker may execute arbitrary commands as the MultiTail process user
- The monitored host or container could be compromised
- Confidential log data could be accessed or modified
- Credentials, tokens, or other process-accessible secrets could be exposed
- The process could be used for further lateral movement, depending on its privileges
General mitigation guidance
Mitigation generally focuses on avoiding shell interpretation of dynamic log content and reducing trust in monitored input.
Common defensive patterns include:
- Prefer direct process execution with an argument array rather than constructing a command string for
sh -c - Treat matched log content as data and keep it separate from executable command structure
- Apply context-aware, complete escaping only where shell execution is unavoidable
- Restrict execute-on-match features to trusted input sources and narrowly defined actions
- Run MultiTail with the minimum filesystem, network, and operating-system privileges required
- Use sandboxing or isolation controls to limit consequences if command execution is reached
- Monitor and constrain configuration changes that enable command execution
Mitigation generally focuses on avoiding shell interpretation of dynamic log content and reducing trust in monitored input.
Common defensive patterns include:
- Prefer direct process execution with an argument array rather than constructing a command string for
sh -c - Treat matched log content as data and keep it separate from executable command structure
- Apply context-aware, complete escaping only where shell execution is unavoidable
- Restrict execute-on-match features to trusted input sources and narrowly defined actions
- Run MultiTail with the minimum filesystem, network, and operating-system privileges required
- Use sandboxing or isolation controls to limit consequences if command execution is reached
- Monitor and constrain configuration changes that enable command execution
How teams detect issues like this
Detection approaches can include:
- Static analysis for shell command construction involving log content or other externally influenced strings
- Code review checks for calls to
system,popen,sh -c, or equivalent execution APIs - Searches for incomplete quoting or escaping before shell invocation
- Tests using metacharacter-containing log input to verify that it remains inert
- Runtime monitoring for unexpected child processes spawned by MultiTail
- Policy enforcement that prohibits shell evaluation of dynamic monitoring data
Automated security review tools may help identify command execution paths, but manual analysis is useful for validating escaping and trust boundaries.
Detection approaches can include:
- Static analysis for shell command construction involving log content or other externally influenced strings
- Code review checks for calls to
system,popen,sh -c, or equivalent execution APIs - Searches for incomplete quoting or escaping before shell invocation
- Tests using metacharacter-containing log input to verify that it remains inert
- Runtime monitoring for unexpected child processes spawned by MultiTail
- Policy enforcement that prohibits shell evaluation of dynamic monitoring data
Automated security review tools may help identify command execution paths, but manual analysis is useful for validating escaping and trust boundaries.
