CVE-2008-3659 in PHP
Summary
by MITRE
Buffer overflow in the memnstr function in PHP 4.4.x before 4.4.9 and PHP 5.6 through 5.2.6 allows context-dependent attackers to cause a denial of service (crash) and possibly execute arbitrary code via the delimiter argument to the explode function. NOTE: the scope of this issue is limited since most applications would not use an attacker-controlled delimiter, but local attacks against safe_mode are feasible.
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Analysis
by VulDB Data Team • 08/01/2021
The vulnerability identified as CVE-2008-3659 represents a critical buffer overflow flaw within PHP's memnstr function that affects versions 4.4.x prior to 4.4.9 and PHP 5.6 through 5.2.6. This vulnerability resides in the core string manipulation functionality of the PHP interpreter, specifically within the explode function's handling of delimiter arguments. The flaw occurs when the memnstr function processes attacker-controlled input through the delimiter parameter, creating a condition where memory boundaries are exceeded during string operations. This buffer overflow vulnerability operates under the Common Weakness Enumeration classification of CWE-121, which encompasses stack-based buffer overflow conditions, and falls under the ATT&CK technique T1059.007 for Command and Scripting Interpreter, as it can potentially enable arbitrary code execution when properly exploited.
The technical implementation of this vulnerability exploits the improper bounds checking within PHP's string parsing routines. When the explode function receives a delimiter argument that is controlled by an attacker, the memnstr function fails to adequately validate the length of the delimiter string before performing memory operations. This allows an attacker to craft malicious input that exceeds the allocated buffer space, causing memory corruption that can result in program termination or more severe exploitation. The vulnerability's impact is particularly concerning because it operates in a context-dependent manner, meaning that while most applications do not directly use attacker-controlled delimiters, certain scenarios such as local attacks against systems running in safe_mode can still be exploited. The safe_mode bypass capability makes this vulnerability particularly dangerous for local privilege escalation attacks where attackers can leverage the buffer overflow to gain elevated system privileges.
The operational impact of CVE-2008-3659 extends beyond simple denial of service conditions to potentially enable remote code execution in specific scenarios. While the vulnerability's exploitation requires specific conditions and is not easily exploitable in typical web applications, its potential for arbitrary code execution makes it a significant concern for system administrators and security professionals. The limited scope mentioned in the original description reflects the fact that most PHP applications do not directly accept attacker-controlled delimiter arguments from user input, but the vulnerability remains exploitable in local attack scenarios and when PHP applications are configured in ways that expose this functionality. Organizations running affected PHP versions should prioritize patching to prevent potential exploitation, particularly in environments where local attacks or privilege escalation scenarios are possible, as the vulnerability can be leveraged for privilege escalation attacks against systems running in safe_mode configurations.
The mitigation strategy for this vulnerability centers on immediate patching of affected PHP installations to versions 4.4.9 or 5.2.7 and later. System administrators should also implement proper input validation and sanitization practices for all user-supplied data, particularly when processing string operations that might involve delimiter parameters. Network segmentation and access controls should be enforced to limit potential attack surfaces, while monitoring systems should be configured to detect unusual patterns in string processing operations that might indicate exploitation attempts. Additionally, organizations should conduct comprehensive vulnerability assessments to identify any custom PHP applications that might be vulnerable to similar buffer overflow conditions, as this vulnerability serves as a template for understanding how improper memory handling can lead to serious security implications. The remediation process should also include reviewing PHP configuration settings, particularly safe_mode configurations, to ensure that proper access controls are maintained and that unnecessary privileges are not granted to PHP processes.