CVE-2003-0844 in mod_gzip
Summary
by MITRE
mod_gzip 1.3.26.1a and earlier, and possibly later official versions, when running in debug mode without the Apache log, allows local users to overwrite arbitrary files via (1) a symlink attack on predictable temporary filenames on Unix systems, or (2) an NTFS hard link on Windows systems when the "Strengthen default permissions of internal system objects" policy is not enabled.
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Analysis
by VulDB Data Team • 06/15/2018
The vulnerability identified as CVE-2003-0844 affects the mod_gzip module version 1.3.26.1a and earlier, with potential impacts extending to later official releases. This security flaw manifests specifically when the module operates in debug mode without utilizing the Apache logging mechanism, creating a dangerous condition that exposes systems to local privilege escalation through file manipulation attacks. The issue stems from predictable temporary file naming conventions that enable attackers to exploit system weaknesses through symbolic link or hard link attacks.
The technical implementation of this vulnerability involves the predictable generation of temporary filenames during mod_gzip operations in debug mode. On unix systems, attackers can create symbolic links with predetermined names that match the temporary file patterns used by mod_gzip, allowing them to redirect file writes to arbitrary locations on the filesystem. Similarly on windows systems, when the "Strengthen default permissions of internal system objects" security policy is disabled, attackers can leverage NTFS hard links to achieve the same objective. This represents a classic race condition vulnerability where the timing of file creation and access allows malicious users to manipulate the intended file destination.
The operational impact of this vulnerability extends beyond simple file overwriting capabilities and represents a significant threat to system integrity and confidentiality. Local attackers with minimal privileges can potentially overwrite critical system files, configuration files, or even log files, leading to information disclosure, system compromise, or denial of service conditions. The vulnerability particularly affects web server environments where mod_gzip is used for content compression, making it a target for attackers seeking to exploit web application infrastructure. The combination of predictable temporary file names and the debug mode operation creates a window of opportunity that persists until the module is properly configured or updated.
Security professionals should note that this vulnerability aligns with CWE-367, which addresses time-of-check to time-of-use (TOCTOU) race conditions, and relates to ATT&CK technique T1059 for command and script injection. The flaw demonstrates the importance of proper temporary file handling and the dangers of operating security-critical modules in debug modes without proper access controls. Organizations should implement immediate mitigations including disabling debug mode for mod_gzip, updating to patched versions, and ensuring that system security policies such as the NTFS hard link restrictions are properly enforced. Additionally, regular security audits should verify that temporary file operations do not expose predictable naming patterns that could be exploited by local users.
The vulnerability also highlights fundamental security principles regarding privilege separation and the dangers of predictable resource naming in security-sensitive applications. Systems administrators should review all modules and applications that generate temporary files, ensuring that proper file permissions and unpredictable naming schemes are implemented to prevent similar race condition attacks. This issue serves as a reminder that security controls must be comprehensive and consider all operational modes of software, including debug and development configurations that may be left enabled in production environments.