CVE-2004-1808 in Metamail
Summary
by MITRE
Extcompose in metamail does not verify the output file before writing to it, which allows local users to overwrite arbitrary files via a symlink attack.
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Analysis
by VulDB Data Team • 06/22/2018
The vulnerability described in CVE-2004-1808 resides within the extcompose component of metamail, a widely used email handling utility in Unix-like systems during the early 2000s. This flaw represents a classic race condition and privilege escalation issue that exploits the insecure handling of temporary files during the composition of email messages. The vulnerability specifically affects systems where metamail is installed with setuid permissions, allowing local users to potentially escalate their privileges or compromise system integrity through careful manipulation of file system permissions and symbolic links.
The technical root cause of this vulnerability stems from improper input validation and file handling within the extcompose utility. When metamail processes email compositions, it creates temporary output files without verifying their existence or ownership before writing data to them. This behavior creates a window of opportunity for malicious users to establish symbolic links with specific names in directories where metamail expects to create its output files. The vulnerability is particularly dangerous because it allows attackers to overwrite any file that the metamail process has write permissions to, potentially including system configuration files, binaries, or other sensitive data.
From an operational impact perspective, this vulnerability presents a significant security risk for systems where metamail is used in multi-user environments with elevated privileges. Attackers can exploit this weakness to overwrite critical system files, modify user permissions, or even inject malicious code into executables that are later executed by the system. The attack vector is particularly insidious because it requires minimal privileges initially - local users can leverage this flaw to potentially escalate their access level and gain unauthorized control over system resources. The vulnerability affects systems where metamail is installed with setuid root permissions, making it a prime target for privilege escalation attacks.
The security implications extend beyond simple file overwriting through the potential for more sophisticated attacks such as privilege escalation and system compromise. According to the CWE taxonomy, this vulnerability maps to CWE-367, which describes a Time-of-Check to Time-of-Use (TOCTOU) race condition. The ATT&CK framework categorizes this as a privilege escalation technique under the T1068 category, where adversaries exploit weaknesses in file handling to gain elevated system access. The vulnerability also aligns with T1548.001, which covers abuse of elevated privileges, and demonstrates how seemingly benign file operations can become critical attack vectors when proper security controls are absent.
Mitigation strategies for this vulnerability should focus on immediate patching and system hardening measures. The most effective solution involves updating to a patched version of metamail where proper file validation and atomic file creation mechanisms have been implemented. System administrators should also implement proper file system permissions, ensuring that metamail is not installed with unnecessary setuid privileges, and that temporary directories have restricted write permissions. Additionally, monitoring for unauthorized symbolic link creation in directories used by email processing utilities can help detect potential exploitation attempts. The vulnerability serves as a reminder of the importance of secure coding practices, particularly in utilities that handle user input and interact with the file system in privileged contexts, emphasizing the need for proper validation and atomic operations to prevent race condition exploitation.