CVE-2012-1823 in Plesk
Summary
by MITRE
sapi/cgi/cgi_main.c in PHP before 5.3.12 and 5.4.x before 5.4.2, when configured as a CGI script (aka php-cgi), does not properly handle query strings that lack an = (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.
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Analysis
by VulDB Data Team • 04/22/2026
The vulnerability identified as CVE-2012-1823 represents a critical security flaw in PHP's CGI implementation that has significant implications for web server configurations. This vulnerability specifically affects PHP versions prior to 5.3.12 and 5.4.2 when PHP is configured to operate as a CGI script rather than through web server modules. The flaw stems from improper handling of query strings within the sapi/cgi/cgi_main.c component of PHP's source code, creating a pathway for remote code execution that directly impacts the security posture of affected systems.
The technical root cause of this vulnerability lies in the insufficient validation of query string parameters within PHP's CGI interface. When PHP processes requests through CGI mode, it uses a function called php_getopt to parse command-line options from the query string. However, the implementation fails to properly skip the php_getopt processing for the 'd' case when query strings lack the required '=' character. This omission allows attackers to inject command-line options directly into the query string, effectively bypassing normal input validation mechanisms. The vulnerability specifically exploits the absence of proper string parsing for parameters that do not contain equals signs, enabling attackers to manipulate PHP's internal option parsing routines.
The operational impact of this vulnerability is severe and far-reaching, as it enables remote attackers to execute arbitrary code on affected systems without authentication. Attackers can leverage this flaw by crafting specially formatted URLs that contain command-line options in the query string, potentially allowing them to modify PHP configuration settings, execute system commands, or even gain full control over the affected web server. This vulnerability is particularly dangerous in shared hosting environments or multi-tenant configurations where multiple users share the same PHP instance, as it could enable privilege escalation or lateral movement within the network infrastructure. The attack vector is straightforward and requires minimal expertise to exploit, making it a high-priority target for malicious actors.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to PHP versions 5.3.12 or 5.4.2, which contain the necessary patches to address the improper query string handling. System administrators should also consider implementing web application firewalls to detect and block suspicious query string patterns, and should review their PHP configurations to ensure that CGI mode is not unnecessarily enabled when alternative modules are available. Additionally, monitoring logs for unusual query string patterns and implementing proper input validation at the web server level can help detect exploitation attempts. This vulnerability aligns with CWE-20, representing a weakness in input validation, and maps to ATT&CK technique T1059 for executing malicious code through command injection, making it a critical component of any comprehensive security assessment.