CVE-2015-3238 in SPARC Enterprise Server
Summary
by MITRE
The _unix_run_helper_binary function in the pam_unix module in Linux-PAM (aka pam) before 1.2.1, when unable to directly access passwords, allows local users to enumerate usernames or cause a denial of service (hang) via a large password.
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Analysis
by VulDB Data Team • 10/20/2018
The vulnerability identified as CVE-2015-3238 affects the pam_unix module in Linux-PAM versions prior to 1.2.1, specifically targeting the _unix_run_helper_binary function. This flaw represents a significant security weakness that can be exploited by local attackers to gain information about system users or disrupt system availability. The vulnerability manifests when the system is unable to directly access password information, creating a scenario where malicious actors can manipulate password input to trigger unintended behavior. The issue falls under the category of improper input validation and weak error handling within authentication mechanisms.
The technical exploitation of this vulnerability occurs through the manipulation of password input during authentication processes. When the pam_unix module encounters a situation where direct password access is not possible, the _unix_run_helper_binary function fails to properly handle large password inputs. This improper handling creates two distinct attack vectors: username enumeration and denial of service conditions. Attackers can submit excessively large password values to trigger a hang condition that effectively causes a denial of service, preventing legitimate authentication attempts. The vulnerability stems from inadequate input sanitization and error recovery mechanisms within the authentication framework.
The operational impact of CVE-2015-3238 extends beyond simple availability disruption to include potential information disclosure risks. Local attackers who can access the system can leverage this vulnerability to enumerate valid usernames through timing variations or error responses that occur when processing malformed password inputs. This username enumeration capability aligns with attack patterns described in the ATT&CK framework under credential access and privilege escalation techniques. The vulnerability's classification under CWE-20 indicates improper input validation, while its exploitation patterns relate to CWE-400, which covers improper handling of resources that can lead to denial of service conditions. The impact is particularly concerning in multi-user environments where attackers might attempt to map user accounts before launching more sophisticated attacks.
Mitigation strategies for CVE-2015-3238 primarily focus on upgrading to Linux-PAM version 1.2.1 or later, which includes patches addressing the improper input handling in the _unix_run_helper_binary function. System administrators should also implement proper access controls and monitor authentication logs for suspicious activity patterns that might indicate exploitation attempts. Additional defensive measures include configuring password policies to limit input length and implementing intrusion detection systems that can identify anomalous authentication behavior. Organizations should also consider implementing rate limiting for authentication attempts to prevent exploitation of the denial of service component. The vulnerability demonstrates the importance of robust input validation in security-critical components and highlights the need for comprehensive testing of edge cases in authentication systems, particularly those involving helper binaries and external process execution.