CVE-2016-9138 in PHP
Summary
by MITRE
PHP through 5.6.27 and 7.x through 7.0.12 mishandles property modification during __wakeup processing, which allows remote attackers to cause a denial of service or possibly have unspecified other impact via crafted serialized data, as demonstrated by Exception::__toString with DateInterval::__wakeup.
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Analysis
by VulDB Data Team • 10/27/2022
The vulnerability identified as CVE-2016-9138 represents a critical flaw in PHP's serialization mechanism that affects versions through 5.6.27 and 7.x through 7.0.12. This issue stems from improper handling of property modifications during the __wakeup processing phase of object deserialization, creating a fundamental weakness in PHP's object lifecycle management. The vulnerability specifically manifests when crafted serialized data triggers unexpected behavior during the reconstruction of objects, particularly involving the Exception::__toString method combined with DateInterval::__wakeup operations. This flaw falls under the category of improper handling of object state during deserialization, which is a well-documented pattern that can lead to severe security implications.
The technical exploitation of this vulnerability occurs through the manipulation of serialized PHP objects where attackers can craft malicious data that, when deserialized, triggers unexpected modifications to object properties during the __wakeup method execution. When PHP encounters a serialized object that implements the __wakeup magic method, it typically executes this method after deserialization to restore object state. However, in this case, the vulnerability allows attackers to modify properties in ways that can cause the application to crash or behave unpredictably. The specific combination of Exception::__toString with DateInterval::__wakeup creates a scenario where the object's internal state can be manipulated in a manner that leads to denial of service conditions or potentially more severe consequences. This represents a classic example of how improper object state management can lead to system instability.
The operational impact of CVE-2016-9138 extends beyond simple denial of service to potentially enable more sophisticated attacks depending on the application's context and how it handles serialized data. When applications deserialize user-provided data without proper validation, attackers can leverage this vulnerability to cause application crashes, leading to availability issues that can disrupt service operations. The unspecified other impacts mentioned in the CVE description suggest that under certain conditions, this vulnerability could potentially be exploited to achieve privilege escalation or information disclosure, though the primary concern remains the denial of service aspect. This vulnerability is particularly dangerous in web applications that accept serialized data from untrusted sources, as it can be triggered through various attack vectors including file uploads, API endpoints, or session data handling.
Mitigation strategies for CVE-2016-9138 focus primarily on updating PHP installations to versions that contain the fix, which was implemented in PHP 5.6.28 and 7.0.13. Organizations should prioritize patching affected systems and conducting thorough vulnerability assessments to identify all instances where serialized data might be processed from untrusted sources. Additionally, implementing strict input validation and sanitization measures can help reduce the attack surface, though the most effective approach remains maintaining up-to-date software versions. Security practitioners should also consider implementing monitoring and logging for deserialization operations to detect potential exploitation attempts. From an ATT&CK perspective, this vulnerability aligns with techniques involving deserialization of untrusted data and privilege escalation, making it a critical consideration for organizations implementing security controls. The vulnerability also relates to CWE-502 which specifically addresses deserialization of untrusted data, highlighting the importance of proper object state management during serialization and deserialization processes.