CVE-2008-2516 in libpam-pgsql
Summary
by MITRE
pam_sm_authenticate in pam_pgsql.c in libpam-pgsql 0.6.3 does not properly consider operator precedence when evaluating the success of a pam_get_pass function call, which allows local users to gain privileges via a SIGINT signal when this function is executing, as demonstrated by a CTRL-C sequence at a sudo password prompt in an "auth sufficient pam_pgsql.so" configuration.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 09/25/2018
The vulnerability described in CVE-2008-2516 resides within the libpam-pgsql 0.6.3 library, specifically in the pam_sm_authenticate function implementation within pam_pgsql.c. This flaw represents a critical security weakness that exploits improper operator precedence during authentication processing, creating a privilege escalation vector for local attackers. The vulnerability manifests when the pam_get_pass function is executed and receives a SIGINT signal, typically generated by pressing CTRL-C, which occurs during authentication processes such as sudo password prompts when the pam_pgsql module is configured with "auth sufficient" directive.
The technical root cause stems from a programming error where the code fails to properly handle the logical evaluation sequence during authentication success determination. When pam_get_pass executes and encounters a SIGINT signal, the improper operator precedence causes the authentication logic to incorrectly evaluate the function's return status, potentially bypassing security checks and allowing unauthorized privilege escalation. This issue is particularly dangerous because it leverages the standard signal handling mechanisms that users expect to work normally during interactive authentication sessions.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it directly compromises the integrity of authentication mechanisms that rely on libpam-pgsql. Attackers can exploit this weakness to gain elevated system privileges without proper authentication, potentially leading to complete system compromise. The vulnerability is particularly concerning in environments where sudo commands are frequently used and where pam_pgsql is configured as an authentication module, as demonstrated by the specific scenario involving CTRL-C sequences at sudo prompts. This creates a realistic attack vector where legitimate users could be exploited through seemingly benign actions like interrupting authentication processes.
Security professionals should recognize this vulnerability as a classic example of improper error handling and operator precedence flaws that can have severe consequences in authentication systems. The issue aligns with CWE-755 weakness classification, which covers improper handling of exceptional conditions that can lead to security vulnerabilities. Organizations should implement immediate mitigations including upgrading to patched versions of libpam-pgsql, reviewing all PAM configurations that utilize this module, and ensuring proper signal handling in authentication workflows. Additionally, system administrators should consider alternative authentication modules or additional security controls when implementing database-based authentication mechanisms to prevent similar vulnerabilities from being exploited in other components of the authentication stack.