CVE-2010-3435 in Linux-PAM
Summary
by MITRE
The (1) pam_env and (2) pam_mail modules in Linux-PAM (aka pam) before 1.1.2 use root privileges during read access to files and directories that belong to arbitrary user accounts, which might allow local users to obtain sensitive information by leveraging this filesystem activity, as demonstrated by a symlink attack on the .pam_environment file in a user s home directory.
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Analysis
by VulDB Data Team • 10/13/2021
The vulnerability identified as CVE-2010-3435 affects the Linux-PAM authentication framework, specifically targeting the pam_env and pam_mail modules. This issue represents a significant privilege escalation concern within the authentication subsystem that could potentially compromise system security. The flaw exists in versions of Linux-PAM prior to 1.1.2, making it a long-standing vulnerability that affected numerous systems running older versions of the authentication framework.
The technical implementation of this vulnerability stems from the improper handling of file access permissions within the pam_env and pam_mail modules. During normal operation, these modules need to read configuration files and mail-related information from user directories. However, the modules execute with elevated root privileges while performing these read operations, even when accessing files belonging to arbitrary user accounts. This design flaw creates an attack surface where local malicious users can manipulate the filesystem to gain unauthorized access to sensitive information that would normally be restricted to specific users.
The operational impact of this vulnerability manifests through symlink attacks that exploit the privilege escalation mechanism. An attacker can create symbolic links in user home directories that point to sensitive system files, such as the .pam_environment file. When the pam_env module attempts to read these files with root privileges, the system follows the symbolic links and exposes the targeted sensitive information to the attacker. This technique allows local users to bypass normal file access controls and potentially extract confidential data that should remain protected within the system's security boundaries.
This vulnerability aligns with CWE-276, which describes improper file permissions, and represents a classic case of privilege escalation through improper access control. The attack vector specifically corresponds to techniques outlined in the ATT&CK framework under privilege escalation tactics, where adversaries leverage system weaknesses to gain elevated access rights. The vulnerability demonstrates how authentication modules can inadvertently create security holes that allow local users to access information they should not normally be able to read, effectively weakening the system's overall security posture.
The mitigation strategy for this vulnerability involves upgrading to Linux-PAM version 1.1.2 or later, which contains the necessary patches to address the privilege escalation issue. System administrators should also implement proper file permission controls and monitor for potential symlink attacks in user directories. Additionally, regular security audits should verify that authentication modules are running with the minimum necessary privileges and that file access operations do not unnecessarily elevate privileges during routine operations. Organizations should consider implementing monitoring solutions that can detect suspicious file access patterns and symbolic link creation activities that might indicate exploitation attempts.