CVE-2008-3660 in PHP
Summary
by MITRE
PHP 4.4.x before 4.4.9, and 5.x through 5.2.6, when used as a FastCGI module, allows remote attackers to cause a denial of service (crash) via a request with multiple dots preceding the extension, as demonstrated using foo..php.
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Analysis
by VulDB Data Team • 08/18/2019
This vulnerability exists in php versions 4.4.x before 4.4.9 and 5.x through 5.2.6 when configured as a FastCGI module. The flaw stems from improper handling of file path resolution in the PHP FastCGI implementation where multiple consecutive dots preceding a file extension are not properly sanitized. When a malicious request is made with a filename containing multiple dots such as foo..php, the PHP FastCGI module fails to correctly process the path traversal logic and subsequently crashes or becomes unresponsive. This represents a classic buffer overflow or memory corruption issue in the file path parsing routine that occurs during the FastCGI request processing phase. The vulnerability is categorized under CWE-121 as a buffer overflow condition and specifically relates to improper input validation in file path handling. The attack vector involves sending a specially crafted HTTP request containing a filename with multiple dots to the vulnerable PHP FastCGI module, which triggers the denial of service condition. The impact extends beyond simple service disruption as this vulnerability can be exploited by remote attackers without authentication, making it particularly dangerous in web server environments. The FastCGI module operates as a persistent process that handles multiple requests, so a single malicious request can cause the entire FastCGI process to crash and potentially affect other concurrent requests. This vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, and specifically targets the service availability aspect of the CIA triad. The flaw demonstrates poor input sanitization practices in the PHP FastCGI implementation where the software fails to properly validate and normalize file paths before processing them. The vulnerability is particularly concerning because FastCGI modules are commonly used in high-traffic web environments where maintaining service availability is critical. When exploited, the vulnerability causes the PHP FastCGI process to terminate unexpectedly, resulting in a complete denial of service for all requests handled by that process. The root cause lies in the lack of proper path normalization and validation within the FastCGI module's file handling code, which fails to account for edge cases involving multiple consecutive dots in filenames. This type of vulnerability is classified as a path traversal attack where the attacker manipulates the file path resolution mechanism to trigger unexpected behavior. The vulnerability affects all versions of PHP prior to 4.4.9 and 5.2.6 when used in FastCGI mode, making it a widespread issue across many production environments. Organizations using PHP in FastCGI configurations should immediately apply the relevant security patches to prevent exploitation. The fix implemented in the patched versions includes enhanced input validation and proper path normalization routines that correctly handle filenames with multiple consecutive dots. This vulnerability also highlights the importance of proper security testing for web server modules, particularly those handling file operations and path resolution. The vulnerability can be easily exploited using standard HTTP request tools and does not require any special privileges or authentication, making it a significant threat to web server availability and reliability. The impact of this vulnerability extends beyond simple denial of service as it can potentially be used as a stepping stone for more complex attacks or as part of a larger exploitation campaign targeting web server infrastructure. Proper configuration and patch management are essential to mitigate this vulnerability and maintain secure web server operations in FastCGI environments.