CVE-2008-4994 in xmcd
Summary
by MITRE
The (1) ncsarmt and (2) ncsawrap scripts in xmcd 2.6 allows local users to overwrite arbitrary files via a symlink attack on a /tmp/Mosaic.*pid temporary file.
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Analysis
by VulDB Data Team • 05/25/2025
The vulnerability identified as CVE-2008-4994 affects the xmcd 2.6 software suite, specifically targeting the ncsarmt and ncsawrap scripts that are part of the Mosaic web browser implementation. This issue represents a classic race condition vulnerability that stems from improper handling of temporary files in a multi-user environment. The flaw allows local attackers to manipulate the system by creating symbolic links that can redirect file operations to arbitrary locations, thereby enabling unauthorized file overwrites and potential privilege escalation. The vulnerability is particularly concerning because it exploits the fundamental security principle of temporary file creation and management in Unix-like systems.
The technical implementation of this vulnerability resides in the improper use of temporary files within the script execution flow. When the ncsarmt and ncsawrap scripts execute, they create temporary files in the /tmp directory with predictable naming patterns such as /tmp/Mosaic.*pid. The vulnerability occurs because these scripts do not properly validate or secure the temporary file creation process, allowing malicious users to establish symbolic links with the same names before the legitimate script creates them. This race condition creates a window where an attacker can control what files are written to during the script execution, enabling them to overwrite any file on the system that the script process has write permissions for. The vulnerability is classified as a symlink attack or race condition, which is categorized under CWE-367 in the Common Weakness Enumeration framework.
The operational impact of this vulnerability extends beyond simple file overwrites to potentially enable more serious security breaches. Local attackers can leverage this weakness to modify critical system files, configuration data, or even executable binaries that the script process might write to. The attack vector requires local system access but does not need elevated privileges initially, making it particularly dangerous in multi-user environments where users might have legitimate access to the affected scripts. When combined with other privilege escalation techniques, this vulnerability could allow attackers to gain higher system privileges or compromise the integrity of the entire system. The attack can be executed by simply creating a symbolic link in the /tmp directory before the script runs, making it a low-effort, high-impact exploit that can be automated.
Mitigation strategies for CVE-2008-4994 focus on eliminating the race condition through proper temporary file handling practices. The most effective approach involves using secure temporary file creation methods that prevent symbolic link attacks, such as using the mkstemp() system call instead of creating temporary files with predictable names. Additionally, administrators should ensure that the affected scripts run with minimal necessary privileges and that the /tmp directory has appropriate permissions to prevent unauthorized symbolic link creation. Implementing proper file access controls and using file system features like the sticky bit on /tmp directories can also help prevent this type of attack. Organizations should also consider upgrading to newer versions of the xmcd software where these vulnerabilities have been addressed. This vulnerability aligns with ATT&CK technique T1059.007 for executing scripts and T1068 for privilege escalation, making it a significant concern for security operations centers monitoring for local privilege escalation attempts.