CVE-2008-4977 in postfix
Summary
by MITRE
** DISPUTED ** postfix_groups.pl in Postfix 2.5.2 allows local users to overwrite arbitrary files via a symlink attack on the (1) /tmp/postfix_groups.stdout, (2) /tmp/postfix_groups.stderr, and (3) /tmp/postfix_groups.message temporary files. NOTE: the vendor disputes this vulnerability, stating "This is not a real issue ... users would have to edit a script under /usr/lib to enable it."
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Analysis
by VulDB Data Team • 08/07/2024
The vulnerability described in CVE-2008-4977 pertains to a potential security flaw in Postfix version 2.5.2's postfix_groups.pl script, which operates within a Unix-like operating system environment. This script is designed to manage group information for Postfix mail server functionality and is executed with elevated privileges during certain administrative operations. The core issue stems from the script's improper handling of temporary files, specifically those located in the /tmp directory, which creates a path traversal and file overwrite opportunity for local attackers.
The technical flaw manifests through a symlink attack vector that exploits the predictable naming convention of temporary files used by postfix_groups.pl. When the script executes, it creates temporary files named postfix_groups.stdout, postfix_groups.stderr, and postfix_groups.message within the /tmp directory without proper security checks. An attacker with local access can create symbolic links with these exact names in the /tmp directory, pointing to sensitive system files or configuration files. When the script runs and attempts to write to these temporary files, it inadvertently overwrites the target files that the symbolic links point to, rather than creating the intended temporary files.
This vulnerability operates under the context of privilege escalation and file system manipulation, where local users can potentially gain unauthorized access to modify critical system files. The attack requires the attacker to have local shell access and the ability to create symbolic links in the /tmp directory, which is typically world-writable on most Unix systems. The impact extends beyond simple file modification, as attackers could potentially overwrite system configuration files, log files, or even critical binaries that the Postfix service depends upon, leading to service disruption or potential privilege escalation.
The operational impact of this vulnerability is significant for systems running Postfix 2.5.2, particularly in environments where multiple users share the same system or where system administrators do not properly monitor file system permissions. The vulnerability allows for persistent modifications to system files that could go unnoticed for extended periods, potentially enabling attackers to establish backdoors or disable security features. The attack vector is particularly concerning because it does not require network access or specialized tools beyond basic shell commands, making it accessible to attackers with minimal technical expertise.
The vendor's response dismissing this as "not a real issue" reflects a common debate in security circles regarding the severity of local privilege escalation vulnerabilities. However, from a cybersecurity perspective, any vulnerability that allows local users to overwrite arbitrary files represents a legitimate concern, especially when considering the potential for chaining with other exploits or the possibility of privilege escalation to root access. This vulnerability aligns with CWE-367 weakness category, which addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and could potentially map to ATT&CK techniques involving privilege escalation and persistence through file modification. The issue demonstrates the importance of proper temporary file handling and the principle of least privilege in system administration, where scripts should not create predictable temporary files in world-writable directories without appropriate security measures.
The recommended mitigations for this vulnerability include immediate patching of Postfix installations to versions that address the temporary file handling issue, implementing proper file permissions on temporary directories, and monitoring for unauthorized symbolic link creation. System administrators should also consider implementing additional security controls such as immutable file attributes on critical system files, regular file integrity checks, and monitoring for suspicious file creation patterns in the /tmp directory. The vulnerability serves as a reminder of the importance of secure coding practices and the need for thorough security reviews of system scripts, particularly those that operate with elevated privileges and interact with the file system.