CVE-2007-2844 in PHP
Summary
by MITRE
PHP 4.x and 5.x before 5.2.1, when running on multi-threaded systems, does not ensure thread safety for libc crypt function calls using protection schemes such as a mutex, which creates race conditions that allow remote attackers to overwrite internal program memory and gain system access.
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Analysis
by VulDB Data Team • 07/20/2021
The vulnerability described in CVE-2007-2844 represents a critical thread safety flaw in PHP versions 4.x and 5.x prior to 5.2.1 when executed on multi-threaded systems. This issue stems from the improper handling of libc crypt function calls within a multi-threaded environment, creating conditions where concurrent access to shared resources can lead to memory corruption and privilege escalation. The flaw specifically affects systems where PHP operates in multi-threaded modes such as Apache with worker or event modules, or other multi-threaded web server configurations.
The technical root cause of this vulnerability lies in the absence of proper synchronization mechanisms when calling the libc crypt function, which is commonly used for password hashing in PHP applications. When multiple threads attempt to invoke the crypt function simultaneously, the lack of mutex protection or similar thread synchronization primitives allows race conditions to occur. These race conditions manifest when threads interfere with each other's execution, potentially causing the crypt function to overwrite critical internal program memory structures. The vulnerability is particularly dangerous because it operates at the system level rather than application level, affecting the underlying runtime environment itself.
The operational impact of CVE-2007-2844 is severe and potentially catastrophic for affected systems. Remote attackers can exploit this vulnerability to overwrite internal program memory, which may lead to arbitrary code execution with the privileges of the web server process. This could result in complete system compromise, data exfiltration, or the establishment of persistent backdoors. The vulnerability is especially dangerous in multi-threaded web server environments where multiple concurrent requests are common, as the race conditions are more likely to occur under high load conditions. Attackers can leverage this flaw to bypass authentication mechanisms, escalate privileges, and gain unauthorized access to sensitive system resources.
This vulnerability maps directly to CWE-362, which describes "Concurrent Execution using Shared Resource with Improper Synchronization," and also relates to CWE-121, "Stack-based Buffer Overflow," as the memory corruption can lead to buffer overflow conditions. From an ATT&CK framework perspective, this vulnerability aligns with T1068, "Exploitation for Privilege Escalation," and T1210, "Exploitation of Remote Services," as it enables attackers to exploit a service running on a web server to gain elevated privileges. The vulnerability also relates to T1190, "Exploitation of Remote Services," and T1072, "Software Deployment Tools," when considering the exploitation of web server software configurations.
Mitigation strategies for CVE-2007-2844 require immediate action to address the core thread safety issue. The most effective solution is to upgrade to PHP 5.2.1 or later versions, which include proper thread safety mechanisms for libc crypt function calls. Organizations should also consider implementing proper thread synchronization in their web server configurations, such as switching from multi-threaded to multi-process models where possible. Additionally, implementing strict access controls, network segmentation, and monitoring for suspicious activities can help detect and prevent exploitation attempts. System administrators should also regularly audit their PHP configurations and ensure that all web applications are running on patched versions of the PHP runtime environment to prevent similar vulnerabilities from being exploited.