CVE-2011-0441 in PHP
Summary
by MITRE
The Debian GNU/Linux /etc/cron.d/php5 cron job for PHP 5.3.5 allows local users to delete arbitrary files via a symlink attack on a directory under /var/lib/php5/.
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Analysis
by VulDB Data Team • 10/21/2021
The vulnerability described in CVE-2011-0441 represents a critical local privilege escalation and file deletion flaw affecting Debian GNU/Linux systems running PHP 5.3.5. This issue stems from a poorly designed cron job configuration that creates security risks through inadequate file handling mechanisms. The vulnerability specifically targets the /etc/cron.d/php5 file which manages periodic PHP maintenance tasks, making it a persistent threat that operates automatically without user intervention.
The technical flaw manifests through a symlink attack vector that exploits the insecure directory handling within the PHP cron job implementation. When the cron job executes, it attempts to create or access files in the /var/lib/php5/ directory structure, but due to insufficient validation of symbolic links, an attacker can manipulate the filesystem to redirect operations to arbitrary locations. This occurs because the cron job does not properly verify that the target directory is a legitimate, non-symlinked location before performing file operations. The vulnerability is classified as a directory traversal attack that leverages the weakness in path resolution mechanisms.
The operational impact of this vulnerability extends beyond simple file deletion to potentially enable broader system compromise. Local attackers with basic user privileges can exploit this flaw to remove critical system files, corrupt application data, or even create malicious files in sensitive locations. The automated nature of cron jobs means that this vulnerability can be exploited repeatedly without requiring user interaction, making it particularly dangerous for systems where regular maintenance tasks are performed. Attackers can use this technique to escalate privileges, disrupt services, or create persistent backdoors within the system.
Mitigation strategies for CVE-2011-0441 require immediate system hardening measures including patching the affected PHP version to a secure release that addresses the symlink handling issue. System administrators should also implement proper directory permissions and ownership controls to prevent unauthorized symbolic link creation in critical system paths. The recommended approach involves modifying the cron job configuration to validate directory integrity before file operations and implementing proper file access controls using unix permissions and capabilities. Additionally, organizations should conduct comprehensive security audits to identify and remediate similar vulnerabilities in other scheduled maintenance tasks and system components. This vulnerability aligns with CWE-367, which addresses time-of-check to time-of-use (TOCTOU) race conditions, and represents a classic example of how insecure temporary file handling can lead to privilege escalation attacks. The attack pattern follows common techniques documented in the ATT&CK framework under privilege escalation and persistence tactics, making it a significant concern for enterprise security teams managing multiple Debian-based systems.