Summary
pfSense CE through 2.9.0 contains an operating system command injection flaw in the OpenVPN connection script. An authenticated VPN user may be able to execute commands with root privileges by supplying a crafted username when the connection or disconnection workflow processes it.
pfSense CE through 2.9.0 contains an operating system command injection flaw in the OpenVPN connection script. An authenticated VPN user may be able to execute commands with root privileges by supplying a crafted username when the connection or disconnection workflow processes it.
Affected context
The vulnerability occurs in pfSense CE deployments that use the affected OpenVPN connection workflow with authenticated users supplied through RADIUS or LDAP. Risk arises when a username containing shell-sensitive characters is incorporated into an eval-processed firewall anchor command during VPN connection or disconnection handling.
The vulnerability occurs in pfSense CE deployments that use the affected OpenVPN connection workflow with authenticated users supplied through RADIUS or LDAP. Risk arises when a username containing shell-sensitive characters is incorporated into an eval-processed firewall anchor command during VPN connection or disconnection handling.
Exploit preconditions
- Attack surface: The OpenVPN connection and disconnection handling scripts
- Required access: Valid authentication as a VPN user through a configured identity provider such as RADIUS or LDAP
- Trigger point: Processing of the authenticated username during OpenVPN session setup or teardown
- Why exploitation is possible: User-controlled username data reaches shell evaluation without sufficient neutralization, allowing command syntax to escape its intended argument context
- Attack surface: The OpenVPN connection and disconnection handling scripts
- Required access: Valid authentication as a VPN user through a configured identity provider such as RADIUS or LDAP
- Trigger point: Processing of the authenticated username during OpenVPN session setup or teardown
- Why exploitation is possible: User-controlled username data reaches shell evaluation without sufficient neutralization, allowing command syntax to escape its intended argument context
Why this happens
The underlying bug is OS command injection caused by placing attacker-influenced username data into a shell command that is evaluated dynamically. Shell metacharacters and quoting constructs can alter the intended command structure when input is not treated strictly as data. This behavior maps to CWE-78: Improper Neutralization of Special Elements used in an OS Command.
The underlying bug is OS command injection caused by placing attacker-influenced username data into a shell command that is evaluated dynamically. Shell metacharacters and quoting constructs can alter the intended command structure when input is not treated strictly as data. This behavior maps to CWE-78: Improper Neutralization of Special Elements used in an OS Command.
Potential impact
- An authenticated VPN user could execute arbitrary commands as root
- The firewall appliance could be fully compromised
- Network traffic controls and firewall policies could be modified
- Credentials, configuration data, or connected network resources could be exposed
- The compromised system could be used for persistence or lateral movement
- An authenticated VPN user could execute arbitrary commands as root
- The firewall appliance could be fully compromised
- Network traffic controls and firewall policies could be modified
- Credentials, configuration data, or connected network resources could be exposed
- The compromised system could be used for persistence or lateral movement
General mitigation guidance
Mitigation generally focuses on removing shell interpretation of identity data and reducing the privileges available to connection hooks.
Common defensive patterns include:
- Replacing dynamically evaluated shell commands with direct argument-based process invocation
- Treating usernames and other identity-provider attributes as untrusted input
- Applying strict allowlists for permitted username formats where compatible with deployment requirements
- Avoiding
evaland equivalent string-to-command execution mechanisms - Running VPN hooks with the minimum privileges required and isolating administrative operations
- Applying centralized identity-provider policies that restrict unsafe account-name characters
Mitigation generally focuses on removing shell interpretation of identity data and reducing the privileges available to connection hooks.
Common defensive patterns include:
- Replacing dynamically evaluated shell commands with direct argument-based process invocation
- Treating usernames and other identity-provider attributes as untrusted input
- Applying strict allowlists for permitted username formats where compatible with deployment requirements
- Avoiding
evaland equivalent string-to-command execution mechanisms - Running VPN hooks with the minimum privileges required and isolating administrative operations
- Applying centralized identity-provider policies that restrict unsafe account-name characters
How teams detect issues like this
Detection approaches may include:
- Static analysis rules identifying
eval, shell expansion, and concatenation of user-controlled values into commands - Code review checks for usernames, group names, or directory attributes entering privileged scripts
- Runtime monitoring for unexpected root processes or command activity spawned by OpenVPN hooks
- Audit correlation between VPN authentication events and unusual firewall or system changes
- Policy enforcement that restricts unsafe identity attributes and requires shell-safe process invocation
Detection approaches may include:
- Static analysis rules identifying
eval, shell expansion, and concatenation of user-controlled values into commands - Code review checks for usernames, group names, or directory attributes entering privileged scripts
- Runtime monitoring for unexpected root processes or command activity spawned by OpenVPN hooks
- Audit correlation between VPN authentication events and unusual firewall or system changes
- Policy enforcement that restricts unsafe identity attributes and requires shell-safe process invocation
