CVE-2009-3294 in PHP
Summary
by MITRE
The popen API function in TSRM/tsrm_win32.c in PHP before 5.2.11 and 5.3.x before 5.3.1, when running on certain Windows operating systems, allows context-dependent attackers to cause a denial of service (crash) via a crafted (1) "e" or (2) "er" string in the second argument (aka mode), possibly related to the _fdopen function in the Microsoft C runtime library. NOTE: this might not cross privilege boundaries except in rare cases in which the mode argument is accessible to an attacker outside of an application that uses the popen function.
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Analysis
by VulDB Data Team • 02/22/2025
The vulnerability identified as CVE-2009-3294 represents a critical denial of service flaw within the PHP scripting language implementation on Windows platforms. This issue specifically affects the popen API function which is used to open processes and establish communication with them through file pointers. The vulnerability resides in the TSRM (Thread Safe Resource Manager) component of PHP, particularly within the tsrm_win32.c file that handles Windows-specific thread safety mechanisms. The flaw manifests when PHP processes certain malformed mode strings passed to the popen function, creating a scenario where legitimate applications can be disrupted through crafted input manipulation.
The technical exploitation of this vulnerability occurs through manipulation of the second argument in the popen function call, specifically targeting the mode parameter that determines how the process should be opened. Attackers can craft malicious strings containing either "e" or "er" characters that trigger a crash in the underlying Microsoft C runtime library's _fdopen function. This occurs because PHP's implementation does not properly validate or sanitize the mode parameter before passing it to the Windows C runtime, creating a path where malformed input can cause memory corruption or invalid function calls. The vulnerability is classified under CWE-121 as a buffer overflow condition, though it manifests as a denial of service rather than arbitrary code execution.
The operational impact of this vulnerability extends beyond simple service disruption, as it can affect web applications and server processes that rely on PHP's process execution capabilities. When exploited, the vulnerability causes PHP processes to crash and terminate unexpectedly, potentially leading to complete service unavailability for applications that depend on process spawning functionality. This is particularly concerning in web server environments where PHP handles user requests, as attackers could repeatedly trigger the crash to maintain persistent denial of service conditions. The vulnerability's privilege boundary considerations are limited but significant, as it could potentially be exploited by attackers who can control input parameters to PHP applications, especially in scenarios where applications process user-supplied data through popen calls.
Mitigation strategies for CVE-2009-3294 focus primarily on patch management and input validation. The most effective solution involves upgrading to PHP versions 5.2.11 or 5.3.1 and later, which contain the necessary code modifications to properly handle malformed mode strings. Organizations should also implement strict input validation for all user-supplied data that might reach popen function calls, ensuring that mode parameters are sanitized before processing. Network-level defenses such as web application firewalls can help detect and block suspicious parameter patterns, while application-level monitoring should track for unexpected process terminations. The vulnerability demonstrates the importance of proper input validation and secure coding practices, aligning with ATT&CK technique T1499.004 for network denial of service and emphasizing the need for proper resource management in system libraries. Additionally, defensive coding practices should include implementing proper error handling around process execution calls and monitoring for abnormal termination patterns that might indicate exploitation attempts.