CVE-2016-6290 in Secure Backup
Summary
by MITRE
ext/session/session.c in PHP before 5.5.38, 5.6.x before 5.6.24, and 7.x before 7.0.9 does not properly maintain a certain hash data structure, which allows remote attackers to cause a denial of service (use-after-free) or possibly have unspecified other impact via vectors related to session deserialization.
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Analysis
by VulDB Data Team • 11/29/2022
The vulnerability identified as CVE-2016-6290 represents a critical use-after-free condition within PHP's session handling mechanism that affects multiple version branches including 5.5.38, 5.6.24, and 7.0.9. This flaw exists in the ext/session/session.c file where PHP manages session data structures during serialization and deserialization processes. The vulnerability stems from improper maintenance of hash data structures during session operations, creating opportunities for attackers to manipulate session data in ways that lead to memory corruption. The issue manifests when PHP processes session data that has been serialized and subsequently deserialized, particularly when the session data contains specially crafted malicious payloads. Attackers can exploit this weakness by crafting session data that, when processed by the vulnerable PHP version, triggers memory management errors. The root cause aligns with CWE-416 which describes use-after-free vulnerabilities, where memory is accessed after it has been freed, leading to unpredictable behavior. This vulnerability operates at the intersection of memory management and data serialization processes, making it particularly dangerous in web application environments where session data is routinely processed and stored.
The operational impact of CVE-2016-6290 extends beyond simple denial of service scenarios to potentially enable more sophisticated attacks. Remote attackers can leverage this vulnerability to cause system instability through denial of service conditions, but the use-after-free nature also opens possibilities for arbitrary code execution in certain circumstances. When PHP attempts to access freed memory during session deserialization, the system may crash or behave unpredictably, effectively creating a denial of service condition. However, the memory corruption aspect means that under specific conditions, attackers might be able to manipulate memory contents to execute arbitrary code, though this typically requires additional attack vectors or conditions. The vulnerability's exploitation requires knowledge of PHP's session handling internals and the ability to control session data, making it more challenging to exploit than some other classes of vulnerabilities. This aligns with ATT&CK technique T1210 which covers exploitation of remote services through use-after-free vulnerabilities. The attack surface is particularly wide given that PHP is used across numerous web applications and frameworks, making this vulnerability relevant to a broad range of systems and organizations.
The mitigation strategy for CVE-2016-6290 centers on immediate version updates to PHP releases that contain the necessary patches. Organizations must upgrade to PHP versions 5.5.38, 5.6.24, or 7.0.9 and later, which include fixes addressing the hash data structure maintenance issues in session handling. System administrators should implement comprehensive patch management procedures to ensure all affected PHP installations are updated promptly. Additional defensive measures include implementing proper session data validation and sanitization, monitoring for unusual session behavior, and restricting session data storage locations. Organizations should also consider implementing web application firewalls that can detect and block malicious session data patterns. The vulnerability demonstrates the importance of proper memory management in interpreted languages and highlights the need for regular security assessments of application frameworks. Security teams should conduct vulnerability scans to identify all affected systems and establish monitoring protocols to detect potential exploitation attempts. The fix implemented in patched versions addresses the core hash table management issue during session deserialization, ensuring that memory is properly managed and freed only after all references are removed. This vulnerability serves as a reminder of the critical importance of keeping software updated, particularly in core components like session management that handle user data across multiple application contexts and are frequently targeted by attackers.