CVE-2016-6295 in macOS
Summary
by MITRE
ext/snmp/snmp.c in PHP before 5.5.38, 5.6.x before 5.6.24, and 7.x before 7.0.9 improperly interacts with the unserialize implementation and garbage collection, which allows remote attackers to cause a denial of service (use-after-free and application crash) or possibly have unspecified other impact via crafted serialized data, a related issue to CVE-2016-5773.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-6295 affects PHP versions prior to specific patched releases, specifically impacting the ext/snmp/snmp.c component within the PHP source code. This issue represents a critical security flaw that arises from improper interaction between the SNMP extension's unserialize implementation and PHP's garbage collection mechanisms. The vulnerability manifests when PHP processes crafted serialized data through the SNMP extension, creating conditions that lead to memory management failures and potentially arbitrary code execution. The flaw is particularly dangerous because it can be exploited remotely through web applications that utilize SNMP functionality or unserialize operations with untrusted input.
The technical root cause of this vulnerability stems from a use-after-free condition that occurs during the garbage collection process when PHP handles serialized SNMP objects. When the unserialize function processes maliciously crafted serialized data containing SNMP objects, the extension's internal memory management does not properly handle the reference counting and cleanup of these objects. This improper handling leads to situations where freed memory locations are accessed again, creating a use-after-free vulnerability that can result in application crashes or potentially allow attackers to execute arbitrary code. The vulnerability is classified as a memory safety issue and aligns with CWE-416, which addresses use-after-free conditions in software implementations.
The operational impact of CVE-2016-6295 extends beyond simple denial of service to potentially enable more sophisticated attacks. Remote attackers can leverage this vulnerability to cause application crashes that result in persistent denial of service conditions, making web applications unavailable to legitimate users. In some scenarios, the use-after-free condition may be exploitable to achieve arbitrary code execution, particularly when the freed memory can be manipulated to contain controlled data. The vulnerability affects PHP installations across multiple version lines, including 5.5.x, 5.6.x, and 7.x, making it a widespread concern for organizations maintaining legacy PHP applications. Attackers exploiting this issue can potentially gain unauthorized access to systems or escalate privileges, depending on the execution environment and available privileges.
Mitigation strategies for CVE-2016-6295 require immediate patching of affected PHP installations to versions that include the necessary fixes for the SNMP extension's unserialize handling. Organizations should prioritize updating their PHP environments to versions 5.5.38, 5.6.24, or 7.0.9 and later, which contain the appropriate memory management fixes. Additionally, implementing proper input validation and sanitization measures can help reduce the attack surface by preventing untrusted data from reaching the unserialize functions. Security teams should also consider disabling the SNMP extension when it is not actively required, as this reduces the potential exploitation vectors. The vulnerability demonstrates the importance of proper memory management in extension modules and highlights the need for comprehensive testing of serialization routines against malicious input. Organizations should monitor their PHP installations regularly and maintain updated security patches to prevent similar vulnerabilities from being exploited in their environments.
The vulnerability relates to the ATT&CK technique T1059.007, which involves command and scripting interpreter usage, as exploitation may involve manipulating PHP scripts to trigger the vulnerable unserialize functionality. It also connects to T1499.004, which covers network denial of service attacks, since the primary impact includes application crashes and service unavailability. The memory corruption aspects of the vulnerability align with ATT&CK technique T1068, which covers exploit for privilege escalation, particularly when exploitation leads to code execution. Organizations should implement network segmentation and monitoring to detect potential exploitation attempts, as well as maintain comprehensive incident response procedures for handling such vulnerabilities in production environments. The vulnerability underscores the critical importance of keeping software components updated and properly tested, particularly for extensions that handle untrusted data processing.