CVE-2010-3430 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 perform the required setfsgid and setgroups system calls, which might allow local users to obtain sensitive information by leveraging unintended group permissions, 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-2010-3430 represents a critical privilege escalation flaw within the Linux Pluggable Authentication Modules framework, specifically affecting the pam_env and pam_mail modules in Linux-PAM version 1.1.2. This issue stems from an incomplete remediation of a previous vulnerability identified as CVE-2010-3435, creating a persistent security weakness that allows local attackers to exploit unintended group permissions. The flaw manifests in the privilege-dropping implementation where the system fails to properly execute the required setfsgid and setgroups system calls during the privilege reduction process.
The technical implementation of this vulnerability occurs when the pam modules attempt to drop privileges from root to a regular user context. Normally, when privilege dropping occurs, the system should invoke setfsgid and setgroups system calls to ensure that the effective group ID and supplementary group memberships are properly reset to match the target user's permissions. However, in this case, these critical system calls are omitted, leaving the process with elevated group permissions that it should not possess. This creates a scenario where a local attacker can leverage this improper privilege handling to access files and resources that should be restricted to the target user's group membership.
The operational impact of this vulnerability is particularly significant as demonstrated by the specific attack vector involving symbolic link manipulation of the .pam_environment file in a user's home directory. When a malicious user creates a symbolic link pointing to a sensitive file or directory, the improper privilege dropping allows the pam module to follow the link with elevated group permissions, potentially exposing confidential information or allowing unauthorized access to restricted resources. This attack vector directly relates to the CWE-276 principle of incorrect default permissions, where the system fails to properly enforce access controls after privilege reduction.
The security implications extend beyond simple information disclosure, as this vulnerability can potentially enable more sophisticated attacks by allowing attackers to manipulate group-based access controls. Attackers could exploit this weakness to read files that are normally restricted to specific group memberships, potentially accessing sensitive configuration data, authentication information, or other restricted resources within the system. This vulnerability aligns with ATT&CK technique T1068 which involves exploiting local privilege escalation opportunities, and more specifically targets the privilege escalation domain where attackers attempt to gain higher-level system access through improper privilege handling.
The mitigation strategies for this vulnerability require immediate patching of the Linux-PAM modules to properly implement the setfsgid and setgroups system calls during the privilege dropping process. Organizations should also conduct comprehensive security assessments to identify any other potential privilege escalation vectors within their authentication frameworks. Additionally, system administrators should implement monitoring for unauthorized symbolic link creation in user directories, particularly in locations where authentication modules may access sensitive files. The vulnerability demonstrates the critical importance of proper privilege management in authentication systems and highlights the necessity of thorough testing of security patches to ensure complete remediation of previously identified issues.