CVE-2012-2311 in PHP
Summary
by MITRE
sapi/cgi/cgi_main.c in PHP before 5.3.13 and 5.4.x before 5.4.3, when configured as a CGI script (aka php-cgi), does not properly handle query strings that contain a %3D sequence but no = (equals sign) character, which allows remote attackers to execute arbitrary code by placing command-line options in the query string, related to lack of skipping a certain php_getopt for the d case. NOTE: this vulnerability exists because of an incomplete fix for CVE-2012-1823.
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Analysis
by VulDB Data Team • 12/24/2024
The vulnerability described in CVE-2012-2311 represents a critical remote code execution flaw affecting PHP installations configured as CGI scripts. This vulnerability specifically impacts PHP versions prior to 5.3.13 and 5.4.x versions before 5.4.3, where the application fails to properly sanitize query strings containing encoded equals signs. The flaw stems from an incomplete remediation of the earlier CVE-2012-1823 vulnerability, creating a persistent security gap that attackers can exploit through carefully crafted query parameters. The issue manifests when PHP's CGI interface processes query strings that contain the URL-encoded equals sign %3D without an actual equals character, allowing malicious actors to inject command-line options directly into the query string. This improper handling occurs within the sapi/cgi/cgi_main.c file, which governs how PHP processes requests when operating in CGI mode, making it a fundamental component of the attack vector.
The technical exploitation of this vulnerability relies on PHP's command-line option parsing mechanism, specifically the php_getopt function's handling of the 'd' case parameter. When PHP encounters a query string containing %3D without =, the parsing logic fails to properly skip the php_getopt processing for the d case, which typically handles PHP configuration directives. This failure creates a scenario where attackers can inject arbitrary PHP configuration options or commands through the query string, effectively bypassing normal input validation and execution controls. The vulnerability operates at the core of PHP's CGI interface, where the web server passes request parameters to the PHP interpreter, and the incomplete fix for CVE-2012-1823 left the system vulnerable to this specific parsing edge case. According to CWE-20, this represents a classic input validation flaw where insufficient checks on user-supplied data lead to improper argument handling, while the ATT&CK framework categorizes this under command and control techniques involving remote code execution through web application vulnerabilities.
The operational impact of CVE-2012-2311 is severe and far-reaching, as it allows remote attackers to execute arbitrary code on vulnerable systems without requiring authentication or prior access. This vulnerability can be exploited through simple web requests containing malicious query strings, making it particularly dangerous in publicly accessible web environments. Attackers can leverage this flaw to gain complete control over affected servers, potentially leading to data breaches, system compromise, and further lateral movement within network environments. The vulnerability's persistence across multiple PHP versions demonstrates the complexity of fixing such parsing-related security issues, as the incomplete remediation for CVE-2012-1823 created a new attack surface that attackers could exploit. Organizations running vulnerable PHP CGI installations face significant risk of compromise, particularly in environments where PHP is used to process user input or where web applications do not properly validate or sanitize query parameters before passing them to the PHP interpreter.
Mitigation strategies for CVE-2012-2311 require immediate patching of affected PHP installations to versions 5.3.13 or 5.4.3 and later, which contain the proper fix for this vulnerability. System administrators should also implement web application firewalls and input validation mechanisms to filter out potentially malicious query strings containing URL-encoded characters. Additionally, organizations should consider disabling PHP CGI functionality when not strictly required, as this reduces the attack surface for such vulnerabilities. Regular security audits and vulnerability assessments should be conducted to identify any remaining instances of vulnerable PHP installations, particularly in legacy systems or environments where patching may be delayed. The fix for this vulnerability specifically addresses the improper handling of the php_getopt function for the d case parameter, ensuring that query strings containing %3D without = are properly processed and do not allow injection of command-line options. Security teams should also monitor for similar parsing vulnerabilities in other web application frameworks and ensure that all input processing mechanisms properly validate and sanitize user-supplied data to prevent analogous issues from occurring in other components of their infrastructure.