CVE-2005-2540 in FlatNuke
Summary
by MITRE
CRLF injection vulnerability in FlatNuke 2.5.5 and possibly earlier versions allows remote attackers to execute arbitrary PHP commands via an ASCII char 13 (carriage return) in the signature field, which is injected into a PHP script without a preceding comment character, which can then be executed by a direct request.
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Analysis
by VulDB Data Team • 07/06/2025
The vulnerability identified as CVE-2005-2540 represents a critical CRLF injection flaw affecting FlatNuke 2.5.5 and potentially older versions of this content management system. This vulnerability resides in the handling of user input within the signature field functionality, where the application fails to properly sanitize or validate input containing carriage return characters. The flaw allows remote attackers to inject malicious content that can be executed as PHP code, creating a significant security risk for affected systems.
The technical exploitation of this vulnerability occurs through the manipulation of ASCII character 13, commonly known as the carriage return character, within the signature field. When this character is processed by the FlatNuke application, it enables attackers to inject additional content into PHP scripts without proper sanitization. The vulnerability specifically arises because the application does not properly escape or filter the carriage return character before incorporating user input into executable code contexts. This injection occurs without a preceding comment character, allowing the injected content to be treated as executable PHP code rather than plain text.
The operational impact of this vulnerability extends beyond simple code injection, as it can lead to complete system compromise when attackers leverage the CRLF injection to execute arbitrary PHP commands. This capability allows adversaries to perform actions such as reading sensitive files, executing shell commands, modifying database content, or even establishing persistent backdoors within the affected system. The vulnerability effectively undermines the security boundaries of the FlatNuke application, potentially enabling attackers to gain unauthorized access to server resources and compromise the integrity of the entire web application environment.
Security practitioners should recognize this vulnerability as a variant of CWE-113, which specifically addresses improper neutralization of CRLF characters in HTTP headers and other contexts. The attack vector aligns with ATT&CK technique T1190, which covers the exploitation of vulnerabilities in web applications through injection attacks. Organizations using FlatNuke versions affected by this vulnerability should immediately implement input validation and sanitization measures, including proper escaping of special characters and comprehensive filtering of user input. The recommended mitigations include updating to patched versions of FlatNuke, implementing web application firewalls, and conducting thorough security assessments to identify potential exploitation attempts. Additionally, administrators should review and restrict the privileges of web application users to minimize the potential impact of successful exploitation attempts.