CVE-2016-7480 in PHP
Summary
by MITRE
The SplObjectStorage unserialize implementation in ext/spl/spl_observer.c in PHP before 7.0.12 does not verify that a key is an object, which allows remote attackers to execute arbitrary code or cause a denial of service (uninitialized memory access) via crafted serialized data.
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Analysis
by VulDB Data Team • 10/28/2022
The vulnerability identified as CVE-2016-7480 affects PHP versions prior to 7.0.12 and resides within the SplObjectStorage unserialize implementation located in ext/spl/spl_observer.c. This flaw represents a critical security issue that undermines the integrity of PHP's serialization mechanism and exposes applications to potential remote code execution or denial of service attacks. The vulnerability specifically targets the object storage functionality that PHP provides through the Standard PHP Library, making it particularly dangerous for web applications that rely heavily on object serialization for data persistence or communication.
The technical flaw stems from insufficient input validation during the unserialization process of SplObjectStorage objects. When PHP processes serialized data containing SplObjectStorage objects, the implementation fails to verify that the keys stored within the collection are indeed objects before attempting to use them. This oversight creates a dangerous condition where maliciously crafted serialized data can manipulate the internal structure of SplObjectStorage, leading to memory access violations or arbitrary code execution. The vulnerability operates at the core level of PHP's object handling mechanisms and demonstrates a classic weakness in object-oriented serialization security practices.
The operational impact of this vulnerability extends far beyond simple denial of service scenarios. Remote attackers can exploit this weakness to execute arbitrary code on vulnerable systems, potentially leading to complete system compromise. The vulnerability affects web applications that deserialize user-provided data or data from external sources, particularly those using PHP's serialization features for session management, data caching, or inter-application communication. Given that many PHP applications rely on SplObjectStorage for managing collections of objects, the attack surface for this vulnerability is substantial. The uninitialize memory access issue can also lead to unpredictable behavior and system instability, making it a significant concern for production environments.
Security professionals should note that this vulnerability aligns with CWE-121, which addresses buffer overflow conditions, and relates to ATT&CK technique T1190 for exploitation of vulnerabilities in application software. The flaw represents a type of deserialization vulnerability that has become increasingly common in web applications, emphasizing the importance of proper input validation and secure coding practices. Organizations should prioritize immediate patching of affected PHP installations to mitigate this risk, as the vulnerability can be exploited remotely without authentication. Additionally, implementing proper input sanitization and validation measures for serialized data can provide additional defense-in-depth layers against similar exploitation attempts.
The vulnerability serves as a reminder of the critical importance of secure serialization practices in modern web development. It highlights the need for comprehensive testing of serialization mechanisms and the implementation of robust input validation to prevent attackers from manipulating object structures during unserialization processes. Organizations should conduct thorough security assessments of their PHP applications to identify potential exposure to similar vulnerabilities and ensure that all dependencies and core components are kept up to date with the latest security patches.