CVE-2016-7124 in PHP
Summary
by MITRE
ext/standard/var_unserializer.c in PHP before 5.6.25 and 7.x before 7.0.10 mishandles certain invalid objects, which allows remote attackers to cause a denial of service or possibly have unspecified other impact via crafted serialized data that leads to a (1) __destruct call or (2) magic method call.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability identified as CVE-2016-7124 represents a critical flaw in PHP's serialization handling mechanism that affects versions prior to 5.6.25 and 7.0.10. This issue resides within the ext/standard/var_unserializer.c component of the PHP interpreter, which is responsible for processing serialized data structures. The flaw manifests when the unserialize function encounters malformed or invalid object data, creating a potential attack vector that can be exploited by remote adversaries to manipulate the application's execution flow.
The technical nature of this vulnerability stems from insufficient validation during the deserialization process, specifically when PHP attempts to reconstruct objects from serialized representations. When malformed serialized data contains invalid object references or corrupted structure information, the unserializer fails to properly handle these edge cases, leading to unpredictable behavior that can result in denial of service conditions. The vulnerability is particularly dangerous because it can trigger automatic method calls during the deserialization process, specifically invoking the __destruct magic method or other special methods defined in the class structure.
The operational impact of CVE-2016-7124 extends beyond simple denial of service scenarios, as the flaw can potentially enable more sophisticated attacks depending on how the application handles serialized data. Remote attackers can craft malicious serialized payloads that, when processed by vulnerable PHP applications, may cause the application to crash or behave unpredictably. In some cases, the vulnerability could allow for arbitrary code execution or privilege escalation depending on the application's configuration and the specific magic methods implemented in the affected classes. This makes the vulnerability particularly concerning for web applications that accept serialized data from untrusted sources, such as user input, cookies, or session data.
From a cybersecurity perspective, this vulnerability aligns with CWE-129 and CWE-134 categories, which address issues related to improper input validation and the execution of code from untrusted sources. The attack pattern follows typical exploit methodologies outlined in the MITRE ATT&CK framework under the T1210 technique for exploiting vulnerabilities in software libraries. Organizations running affected PHP versions should immediately implement patch management procedures to upgrade to the fixed versions, as the vulnerability can be exploited without authentication and can be easily automated by malicious actors. Additionally, developers should review their applications for improper handling of serialized data and implement proper input validation and sanitization measures to prevent exploitation of similar vulnerabilities in other components of their systems.