CVE-2016-7411 in macOS
Summary
by MITRE
ext/standard/var_unserializer.re in PHP before 5.6.26 mishandles object-deserialization failures, which allows remote attackers to cause a denial of service (memory corruption) or possibly have unspecified other impact via an unserialize call that references a partially constructed object.
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Analysis
by VulDB Data Team • 10/07/2022
The vulnerability identified as CVE-2016-7411 represents a critical deserialization flaw within the PHP runtime environment that affects versions prior to 5.6.26. This issue resides in the ext/standard/var_unserializer.re component of PHP's standard library, which handles the process of reconstructing objects from serialized data streams. The flaw manifests when the deserialization process encounters objects that are partially constructed or malformed, creating a scenario where the PHP interpreter fails to properly manage memory allocation and object state recovery. This vulnerability is particularly dangerous because it can be exploited through remote code execution channels, making it a significant threat to web applications that rely on PHP for processing user input or data exchange.
The technical nature of this vulnerability stems from improper handling of object deserialization failures within PHP's internal serialization engine. When PHP attempts to unserialize data that references objects which have not been fully constructed or which contain inconsistent state information, the var_unserializer component fails to properly validate the object's integrity before proceeding with memory operations. This leads to memory corruption issues where the interpreter may attempt to access invalid memory locations or manipulate object references in ways that corrupt the application's memory space. The vulnerability is classified under CWE-457 as "Use of Uninitialized Variable" and also relates to CWE-121 as "Stack-based Buffer Overflow" due to the memory corruption aspects of the flaw. The improper object state management during deserialization creates opportunities for attackers to craft malicious serialized data that triggers these memory handling issues.
The operational impact of CVE-2016-7411 extends beyond simple denial of service conditions to potentially enable more severe attacks depending on the application context and system configuration. Remote attackers can leverage this vulnerability to cause application crashes through memory corruption, leading to persistent denial of service conditions that can disrupt legitimate user access to web services. In environments where PHP applications process untrusted input data such as API requests, user uploads, or session data, attackers can construct serialized objects that trigger the vulnerable code path. The unspecified other impacts mentioned in the CVE description suggest potential for privilege escalation or information disclosure scenarios, particularly when the vulnerable PHP application runs with elevated privileges or when memory corruption leads to exploitable conditions within the application's memory space. This vulnerability directly maps to ATT&CK technique T1203 as "Exploitation for Client Execution" and T1499 as "Endpoint Denial of Service" due to its ability to cause system instability and service disruption.
Mitigation strategies for CVE-2016-7411 primarily focus on immediate version updates to PHP 5.6.26 or later releases where the deserialization handling has been corrected. Organizations should implement comprehensive patch management procedures to ensure all PHP installations are updated promptly, as this vulnerability affects the core PHP runtime rather than specific extensions or modules. Additional defensive measures include implementing strict input validation and sanitization for all data that undergoes deserialization, particularly data from external sources or user-controlled inputs. Security practices should emphasize the principle of least privilege for PHP application processes and the implementation of proper error handling and memory management within application code. Network-level protections such as web application firewalls can provide additional layers of defense by monitoring for suspicious serialized data patterns, though these should complement rather than replace proper application-level fixes. The vulnerability also underscores the importance of secure coding practices and thorough testing of deserialization logic within applications, particularly in environments where PHP applications handle external data inputs that require object reconstruction.