CVE-2015-3211 in php-fpm
Summary
by MITRE
php-fpm allows local users to write to or create arbitrary files via a symlink attack.
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Analysis
by VulDB Data Team • 11/10/2019
The vulnerability identified as CVE-2015-3211 affects PHP-FPM (FastCGI Process Manager) implementations and represents a significant local privilege escalation vector through symbolic link manipulation. This flaw enables attackers with local system access to exploit the FastCGI protocol handler and manipulate file system operations by leveraging symlink attacks. The vulnerability stems from insufficient validation of file paths during FastCGI request processing, allowing malicious actors to redirect file operations to unintended destinations.
The technical implementation of this vulnerability occurs within the PHP-FPM daemon where FastCGI requests are processed. When PHP-FPM handles requests that involve file operations, it does not properly validate or sanitize symbolic link references in file paths. Attackers can create malicious symbolic links in directories where PHP-FPM processes files, causing the daemon to write data to arbitrary locations on the file system. This occurs because the FastCGI protocol implementation does not properly resolve symbolic links before performing file operations, creating a path traversal condition that can be exploited to overwrite critical system files or create malicious files with elevated privileges.
From an operational impact perspective, this vulnerability poses severe risks to web server security and system integrity. Local attackers who can execute code on a system running PHP-FPM can leverage this flaw to escalate privileges and gain unauthorized access to sensitive system resources. The attack vector is particularly dangerous because it requires only local system access, making it easier to exploit compared to remote vulnerabilities. The vulnerability can enable attackers to modify PHP configuration files, inject malicious code into web applications, or create backdoor accounts. Additionally, the attack can be used to corrupt system files or manipulate the web server's operational environment, potentially leading to complete system compromise.
The exploitation of CVE-2015-3211 aligns with several ATT&CK tactics including privilege escalation and persistence, as attackers can use the vulnerability to gain elevated privileges and establish long-term access to compromised systems. This vulnerability is classified under CWE-367 which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) flaws in file operations, where the system checks file permissions or existence at one point in time but then performs operations on the file at a later point when conditions may have changed. The vulnerability also relates to CWE-22 which covers improper limitation of a pathname to a restricted directory, or Path Traversal attacks that can be exploited through symbolic link manipulation. Organizations should implement immediate mitigations including updating to patched versions of PHP-FPM, implementing proper file system permissions, and monitoring for unauthorized symbolic link creation in web server directories. System administrators should also consider implementing file integrity monitoring solutions to detect unauthorized file modifications and ensure proper sandboxing of PHP-FPM processes to prevent privilege escalation through file system manipulation.