CVE-2014-9425 in PHP
Summary
by MITRE
Double free vulnerability in the zend_ts_hash_graceful_destroy function in zend_ts_hash.c in the Zend Engine in PHP through 5.5.20 and 5.6.x through 5.6.4 allows remote attackers to cause a denial of service or possibly have unspecified other impact via unknown vectors.
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Analysis
by VulDB Data Team • 03/01/2022
The CVE-2014-9425 vulnerability represents a critical double free condition within the Zend Engine's thread-safe hash table destruction mechanism. This flaw exists in the zend_ts_hash_graceful_destroy function located in zend_ts_hash.c, affecting PHP versions up to 5.5.20 and 5.6.x through 5.6.4. The vulnerability manifests when the engine processes certain hash table structures during cleanup operations, creating a scenario where memory allocated for hash table elements is freed twice, potentially leading to memory corruption and system instability.
The technical implementation of this vulnerability exploits the thread-safe hash table management system that PHP employs to handle concurrent access to hash data structures. When the zend_ts_hash_graceful_destroy function processes hash tables containing specific configurations or data patterns, it fails to properly track memory allocation states, resulting in the same memory block being deallocated twice. This double free condition occurs during the graceful destruction phase of hash table structures, where the engine attempts to clean up resources while maintaining thread safety through its internal locking mechanisms.
From an operational perspective, this vulnerability presents significant risks to web application security and system stability. Remote attackers can potentially exploit this issue to trigger denial of service conditions by causing the PHP process to crash or become unresponsive. The impact extends beyond simple service disruption, as the double free condition could theoretically be leveraged to execute arbitrary code or cause additional unspecified security impacts, making it particularly dangerous in web server environments where PHP processes handle untrusted input from external sources. The vulnerability's remote exploitability means that attackers do not require local system access to potentially compromise affected systems.
The underlying cause of this vulnerability aligns with CWE-415, which describes the condition where a program frees the same memory location twice, creating a classic double free error that can be exploited for memory corruption attacks. This flaw demonstrates poor memory management practices within the Zend Engine's hash table implementation, particularly in how it handles reference counting and resource cleanup for thread-safe data structures. The vulnerability operates within the broader context of memory safety issues that affect interpreted languages and their underlying virtual machines.
Security mitigations for this vulnerability primarily involve immediate patching and upgrading to PHP versions that contain the fix for this specific double free condition. Organizations should prioritize updating their PHP installations to versions 5.5.21 or 5.6.5 and later, which contain the necessary code modifications to prevent the double free scenario. Additionally, implementing proper input validation and sanitization measures can help reduce the attack surface, while monitoring for unusual process behavior or memory allocation patterns may help detect exploitation attempts. The remediation process should also include reviewing application code that heavily relies on hash table operations to ensure no custom implementations might interact poorly with the fixed engine components, as this vulnerability could potentially be chained with other memory corruption issues within the same runtime environment.