CVE-2008-4936 in mgetty
Summary
by MITRE
faxspool in mgetty 1.1.36 allows local users to overwrite arbitrary files via a symlink attack on a /tmp/faxsp.##### temporary file.
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Analysis
by VulDB Data Team • 08/22/2019
The vulnerability identified as CVE-2008-4936 resides within the faxspool component of mgetty version 1.1.36, representing a classic race condition and symbolic link attack scenario that enables local privilege escalation. This flaw specifically targets the temporary file creation process where the faxspool utility generates temporary files in the /tmp directory with predictable naming patterns such as faxsp.#####. The vulnerability stems from insufficient input validation and improper file handling mechanisms that fail to verify the existence and ownership of these temporary files before writing to them, creating a window of opportunity for malicious users to exploit the system.
The technical exploitation of this vulnerability occurs through a carefully orchestrated symlink attack where an attacker creates symbolic links with the same names as the temporary files that mgetty will subsequently create. When the faxspool utility runs with elevated privileges, it processes these temporary files without proper verification, allowing the attacker to control what data gets written to arbitrary locations on the filesystem. This represents a fundamental failure in secure file handling practices and violates the principle of least privilege, as the utility should not be able to overwrite files outside of its intended scope without proper authorization checks.
The operational impact of this vulnerability extends beyond simple file overwriting, as it provides a pathway for local users to potentially escalate their privileges or corrupt system files. Attackers could leverage this weakness to overwrite critical system binaries, configuration files, or log files, potentially leading to persistent backdoors or system instability. The vulnerability affects systems where mgetty is installed and running with elevated privileges, making it particularly dangerous in multi-user environments where local users might not have direct access to system resources but can still exploit this weakness to gain unauthorized access to sensitive areas of the filesystem.
This vulnerability aligns with CWE-367, which describes the "Time-of-Check to Time-of-Use (TOCTOU) race condition" and corresponds to ATT&CK technique T1068, which covers "Local Privilege Escalation." The flaw demonstrates poor file system security practices and inadequate protection against symbolic link manipulation, which are common attack vectors in Unix-like systems. Organizations should implement proper file validation procedures, use secure temporary file creation methods such as mkstemp(), and ensure that all temporary files are created with appropriate permissions and ownership checks. Additionally, system administrators should consider disabling unnecessary services like mgetty if fax functionality is not required, and regularly audit system configurations to prevent similar race condition vulnerabilities from persisting in other applications. The remediation strategy should include updating to patched versions of mgetty, implementing proper file access controls, and conducting regular security assessments to identify and address similar weaknesses in system utilities that handle temporary files or user input.