CVE-2011-3628 in Ubuntu Linux
Summary
by MITRE
Untrusted search path vulnerability in pam_motd (aka the MOTD module) in libpam-modules before 1.1.3-2ubuntu2.1 on Ubuntu 11.10, before 1.1.2-2ubuntu8.4 on Ubuntu 11.04, before 1.1.1-4ubuntu2.4 on Ubuntu 10.10, before 1.1.1-2ubuntu5.4 on Ubuntu 10.04 LTS, and before 0.99.7.1-5ubuntu6.5 on Ubuntu 8.04 LTS, when using certain configurations such as "session optional pam_motd.so", allows local users to gain privileges by modifying the PATH environment variable to reference a malicious command, as demonstrated via uname.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 05/10/2026
The vulnerability described in CVE-2011-3628 represents a critical untrusted search path weakness within the Pluggable Authentication Modules (PAM) framework, specifically affecting the MOTD (Message of the Day) module. This flaw exists in libpam-modules versions prior to the specified patches across multiple Ubuntu LTS and non-LTS releases, creating a persistent security risk for systems utilizing PAM authentication with the pam_motd module. The vulnerability stems from improper handling of the PATH environment variable during module execution, allowing local attackers to manipulate system behavior through environment variable manipulation.
The technical flaw manifests when the pam_motd module executes external commands without properly sanitizing the execution environment, particularly the PATH variable that determines command resolution order. When systems configure PAM sessions with "session optional pam_motd.so", the module attempts to execute commands such as uname to display system information in the message of the day. However, due to the untrusted search path implementation, attackers can prepend malicious directories to the PATH variable, causing the system to execute attacker-controlled binaries instead of legitimate system commands. This privilege escalation vector operates under the principle that the module inherits the user's environment, including potentially compromised PATH settings, which violates fundamental security practices for command execution in privileged contexts.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to gain elevated system access through seemingly innocuous configuration files or environment variable modifications. The vulnerability is particularly dangerous because it operates silently without requiring authentication, and the attack surface includes any system utilizing the affected PAM configurations. The specific demonstration using uname command shows how attackers can substitute legitimate system binaries with malicious equivalents, potentially allowing for complete system compromise. This vulnerability aligns with CWE-426 Untrusted Search Path and CWE-78 Improper Neutralization of Special Elements used in OS Command, both of which are classified as high-risk due to their potential for privilege escalation and system compromise.
Mitigation strategies for CVE-2011-3628 require immediate patching of affected systems to the corrected libpam-modules versions, while also implementing additional security measures to prevent environment variable manipulation. Organizations should audit their PAM configurations to identify all instances of pam_motd usage and ensure that such modules are not configured with optional or untrusted execution contexts. The ATT&CK framework categorizes this vulnerability under T1068 Privilege Escalation through Environment Variable Manipulation, where adversaries exploit weak security controls in system execution paths to gain elevated privileges. System administrators should also implement monitoring for suspicious PATH modifications and consider implementing mandatory access controls or SELinux policies to prevent unauthorized environment variable changes that could lead to privilege escalation through the vulnerable PAM module.
The broader implications of this vulnerability highlight the importance of secure coding practices in authentication modules and the critical need for environment variable sanitization in privileged code execution contexts. This flaw demonstrates how seemingly benign system components can become attack vectors when proper security controls are not implemented, particularly in the context of PAM module development where environment inheritance can create unexpected security exposure points. The vulnerability also emphasizes the necessity of regular security updates and the importance of maintaining secure default configurations in authentication frameworks to prevent exploitation of known weaknesses in system components.