CVE-2010-4707 in Linux-PAM
Summary
by MITRE
The check_acl function in pam_xauth.c in the pam_xauth module in Linux-PAM (aka pam) 1.1.2 and earlier does not verify that a certain ACL file is a regular file, which might allow local users to cause a denial of service (resource consumption) via a special file.
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Analysis
by VulDB Data Team • 10/13/2021
The vulnerability identified as CVE-2010-4707 resides within the pam_xauth module of Linux-PAM version 1.1.2 and earlier, specifically within the check_acl function in pam_xauth.c. This flaw represents a classic security oversight where proper file type validation is omitted during access control list processing. The issue manifests when the module fails to verify that an ACL file is actually a regular file before proceeding with access control operations, creating a potential vector for resource exhaustion attacks.
The technical implementation of this vulnerability stems from insufficient input validation within the authentication framework. When the pam_xauth module processes access control lists, it accepts file paths without performing proper file type checks. This omission allows malicious local users to create special files such as symbolic links, character devices, or named pipes that point to resources which, when accessed by the check_acl function, can cause the system to consume excessive resources or enter an infinite loop. The vulnerability operates at the system-level authentication layer, making it particularly dangerous as it can be exploited during legitimate authentication processes.
From an operational impact perspective, this vulnerability enables local privilege escalation and denial of service conditions that can significantly compromise system availability and stability. Attackers can exploit this weakness to consume system resources such as CPU cycles, memory, or file descriptors, potentially leading to system crashes or making the authentication service unavailable to legitimate users. The resource consumption aspect aligns with attack patterns documented in the ATT&CK framework under privilege escalation and denial of service tactics, where adversaries seek to exhaust system resources to disrupt normal operations.
The vulnerability demonstrates characteristics consistent with CWE-59 and CWE-248, representing failures in file validation and improper handling of special files. These weaknesses create a pathway for attackers to manipulate the authentication process and potentially gain unauthorized access to system resources. The impact extends beyond simple resource exhaustion, as the vulnerability can be leveraged to disrupt the normal operation of the PAM framework, affecting all applications that rely on authentication services provided by the module.
Effective mitigation strategies include updating to Linux-PAM versions 1.1.3 and later where the vulnerability has been patched, implementing proper file type validation in the check_acl function, and deploying monitoring solutions to detect unusual resource consumption patterns during authentication processes. System administrators should also consider implementing access controls that limit the ability of local users to create special files in authentication-related directories and ensure proper file permissions are enforced throughout the system. The fix typically involves adding explicit checks to verify that files are regular files before processing their access control lists, preventing the exploitation of this class of vulnerability through symbolic links or other special file types.