CVE-2010-3431 in Linux-PAM
Summary
by MITRE
The privilege-dropping implementation in the (1) pam_env and (2) pam_mail modules in Linux-PAM (aka pam) 1.1.2 does not check the return value of the setfsuid system call, which might allow local users to obtain sensitive information by leveraging an unintended uid, as demonstrated by a symlink attack on the .pam_environment file in a user s home directory. NOTE: this vulnerability exists because of an incomplete fix for CVE-2010-3435.
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Analysis
by VulDB Data Team • 10/13/2021
The vulnerability described in CVE-2010-3431 represents a critical privilege escalation issue within the Linux Pluggable Authentication Modules framework, specifically affecting the pam_env and pam_mail modules in Linux-PAM version 1.1.2. This flaw stems from an incomplete remediation of a previous vulnerability, CVE-2010-3435, creating a persistent security weakness that allows local attackers to exploit improper privilege handling mechanisms. The core issue manifests in the privilege-dropping implementation where the system fails to properly validate the return values of critical system calls, specifically the setfsuid function that manages filesystem user identifiers during authentication processes.
The technical flaw occurs when the pam_env and pam_mail modules attempt to drop privileges from root to a regular user context during authentication operations. The setfsuid system call, which is responsible for setting the filesystem user ID, is called without proper error checking. When this system call fails, it returns a non-zero value indicating an error condition, but the modules continue execution without handling this failure. This oversight creates a scenario where the process maintains elevated privileges longer than intended, potentially allowing malicious actors to manipulate filesystem permissions and access sensitive data. The vulnerability is particularly exploitable through symlink attacks on the .pam_environment file located in user home directories, where attackers can create symbolic links to gain access to files that should normally be restricted to specific users.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides a pathway for local privilege escalation attacks that can compromise the integrity of the authentication system. Attackers can leverage this weakness to read files that contain sensitive authentication information, environment variables, or other data that should remain protected within the user context. The attack vector involving symlink manipulation demonstrates how the incomplete fix for CVE-2010-3435 created a new attack surface where the privilege dropping mechanism fails to properly enforce security boundaries. This vulnerability affects systems using Linux-PAM versions 1.1.2 and potentially earlier versions, making it relevant to a significant portion of enterprise and server environments that rely on standard authentication mechanisms.
Security professionals should note that this vulnerability aligns with CWE-254, which addresses the weakness of inadequate privilege handling in security-critical functions. The issue also maps to ATT&CK technique T1068, which covers the use of privilege escalation techniques to gain higher-level permissions within a system. Organizations should prioritize immediate patching of affected Linux-PAM installations and implement monitoring for unauthorized access attempts to sensitive authentication files. The remediation process requires updating to Linux-PAM versions that properly implement return value checking for setfsuid calls and ensure complete privilege dropping mechanisms are enforced. Additionally, system administrators should conduct thorough audits of authentication module configurations and implement proper file permissions to prevent unauthorized symbolic link creation in user home directories, particularly in areas where sensitive authentication data is stored.