CVE-2016-5726 in Simple Machines Forum
Summary
by MITRE
Packages.php in Simple Machines Forum (SMF) 2.1 allows remote attackers to conduct PHP object injection attacks and execute arbitrary PHP code via the themechanges array parameter.
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Analysis
by VulDB Data Team • 11/12/2022
The vulnerability identified as CVE-2016-5726 resides within the packages.php file of Simple Machines Forum version 2.1, representing a critical security flaw that enables remote attackers to perform PHP object injection attacks. This vulnerability specifically targets the themechanges array parameter, which is processed without adequate input validation or sanitization, creating an exploitable condition that can be leveraged for arbitrary code execution. The flaw stems from improper handling of user-supplied data within the forum's package management system, where serialized PHP objects are directly unserialized without sufficient security checks.
The technical implementation of this vulnerability involves the manipulation of the themechanges array parameter through HTTP requests, allowing attackers to inject malicious PHP objects that get processed by the unserialize() function. When the forum processes these objects, the serialized data gets converted back into PHP objects, executing any malicious code contained within the object's methods or properties. This type of vulnerability falls under CWE-502, which specifically addresses deserialization of untrusted data, and represents a classic example of PHP object injection that has been documented in various security frameworks and threat intelligence reports. The attack vector is particularly dangerous because it operates entirely through web-based interactions, requiring no local system access or privileged accounts.
The operational impact of this vulnerability extends beyond simple code execution, as successful exploitation can lead to complete compromise of the affected forum server. Attackers can leverage this vulnerability to gain unauthorized access to the system, potentially escalating privileges and establishing persistent backdoors. The implications for forum administrators are severe, as compromised systems can be used for data exfiltration, hosting malicious content, or as stepping stones for further attacks within the network infrastructure. This vulnerability particularly affects organizations relying on SMF for community forums, as the attack surface includes not just the forum itself but potentially the entire hosting environment where the application resides.
Mitigation strategies for CVE-2016-5726 should focus on immediate patching of the SMF 2.1 installation to the latest version that addresses this specific vulnerability. Organizations should also implement network-level protections such as web application firewalls that can detect and block suspicious serialization patterns in HTTP requests. Input validation should be strengthened at multiple levels, including implementing strict type checking for array parameters and avoiding direct unserialization of user-provided data. Security monitoring should be enhanced to detect unusual patterns in package management operations, and access controls should be reviewed to ensure that only authorized administrators can perform package modifications. Additionally, the vulnerability demonstrates the importance of following secure coding practices that align with the ATT&CK framework's defense-in-depth principles, particularly in preventing code injection attacks through proper data sanitization and validation mechanisms.