CVE-2011-3148 in Linux-PAM
Summary
by MITRE
Stack-based buffer overflow in the _assemble_line function in modules/pam_env/pam_env.c in Linux-PAM (aka pam) before 1.1.5 allows local users to cause a denial of service (crash) and possibly execute arbitrary code via a long string of white spaces at the beginning of the ~/.pam_environment file.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 12/06/2021
The vulnerability CVE-2011-3148 represents a critical stack-based buffer overflow within the Linux-PAM authentication framework, specifically affecting the _assemble_line function in modules/pam_env/pam_env.c. This flaw exists in Linux-PAM versions prior to 1.1.5 and demonstrates a classic software security weakness that can be exploited by local attackers to compromise system integrity. The vulnerability is particularly concerning because it affects a core authentication module that is widely deployed across Unix-like operating systems, making it a prime target for exploitation in privilege escalation scenarios.
The technical implementation of this vulnerability occurs when the _assemble_line function processes the ~/.pam_environment configuration file without proper bounds checking on input strings. When a maliciously crafted file contains an excessive number of leading whitespace characters, the function fails to validate the buffer size before copying data into a fixed-length stack buffer. This results in memory corruption that can overwrite adjacent stack variables and potentially overwrite the return address of the calling function. The vulnerability is classified as CWE-121 Stack-based Buffer Overflow, which is a well-documented weakness in software development practices that directly violates secure coding principles.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable arbitrary code execution. Local attackers can exploit this flaw by creating a specially crafted ~/.pam_environment file with an excessive number of leading spaces, causing the pam_env module to crash during authentication processes or potentially redirect execution flow to malicious code. This represents a significant threat to system security as authentication mechanisms are fundamental to access control, and compromising them can lead to privilege escalation or complete system compromise. The attack vector is particularly insidious because it requires only local user access and can be triggered during normal authentication workflows.
From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1068 for privilege escalation and T1547 for authentication process manipulation. The exploitability is enhanced by the fact that the vulnerability occurs during routine authentication operations, making it difficult to detect in normal system monitoring. Organizations should prioritize patching this vulnerability immediately, as it represents a persistent threat to authentication security. The recommended mitigation includes upgrading to Linux-PAM version 1.1.5 or later, which implements proper bounds checking and input validation in the affected function. Additionally, system administrators should implement monitoring for unusual authentication patterns and consider implementing mandatory access controls to limit the impact of potential exploitation. The vulnerability underscores the importance of secure coding practices and input validation in authentication modules, as these components form the foundation of system security infrastructure.