CVE-1999-0342 in PAM
Summary
by MITRE
Linux PAM modules allow local users to gain root access using temporary files.
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Analysis
by VulDB Data Team • 04/17/2026
The vulnerability described in CVE-1999-0342 represents a critical privilege escalation flaw within Linux Pluggable Authentication Modules that affected numerous Unix-like systems during the late 1990s. This security issue specifically targeted the way PAM modules handled temporary files during authentication processes, creating a race condition that malicious local users could exploit to gain root privileges. The flaw emerged from improper handling of temporary file creation and access permissions within the PAM framework, which was a fundamental component of system authentication across Linux distributions and other Unix-based operating systems.
The technical implementation of this vulnerability stemmed from the insecure creation of temporary files by PAM modules during authentication operations. When PAM modules executed authentication routines, they would often create temporary files in predictable locations without proper security measures such as secure temporary file creation functions or appropriate permission settings. Attackers could exploit this by creating symbolic links or hard links to target files in system directories, particularly those requiring root privileges for modification. This race condition occurred between the time a PAM module checked for a temporary file's existence and when it actually opened or modified that file, allowing malicious users to manipulate the file contents or replace the temporary file with a crafted alternative. The vulnerability aligns with CWE-377, which addresses insecure temporary file creation practices, and CWE-276, which covers improper file permissions.
The operational impact of this vulnerability was severe and widespread across Linux distributions and Unix systems that relied on PAM for authentication. Local users who previously had limited access to the system could leverage this flaw to escalate their privileges to root level, effectively gaining complete control over the affected systems. This privilege escalation capability meant that attackers could modify system files, install malicious software, create new user accounts with administrative privileges, and potentially access sensitive data without detection. The vulnerability particularly affected systems where PAM modules were used for password authentication, account management, and session handling processes. Organizations running these systems faced significant security risks as the exploit required minimal privileges to execute and could be automated, making it a popular target for malicious actors seeking persistent access to compromised systems.
Mitigation strategies for CVE-1999-0342 required immediate system updates and configuration changes to address the underlying temporary file handling issues within PAM modules. System administrators needed to apply security patches released by Linux vendors and distribution maintainers that corrected the insecure temporary file creation methods used by PAM modules. The recommended approach involved implementing secure temporary file creation practices such as using mkstemp() functions instead of temporary file naming schemes, setting appropriate file permissions for temporary files, and ensuring that temporary files were created with exclusive access modes. Additionally, organizations should have implemented proper file system permissions and monitoring to detect unauthorized temporary file creation attempts. This vulnerability highlighted the importance of secure coding practices in authentication modules and led to enhanced security requirements for system components handling sensitive operations. The incident also reinforced the necessity of regular security audits and updates to prevent exploitation of similar race condition vulnerabilities, aligning with ATT&CK technique T1068 which addresses local privilege escalation through race conditions and improper file handling.