CVE-2006-2878 in DokuWiki
Summary
by MITRE
The spellchecker (spellcheck.php) in DokuWiki 2006/06/04 and earlier allows remote attackers to insert and execute arbitrary PHP code via "complex curly syntax" that is inserted into a regular expression that is processed by preg_replace with the /e (executable) modifier.
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Analysis
by VulDB Data Team • 06/20/2019
The vulnerability described in CVE-2006-2878 represents a critical remote code execution flaw within the DokuWiki content management system. This issue affects versions released on or before June 4, 2006, specifically targeting the spellchecker component known as spellcheck.php. The vulnerability stems from improper input validation and sanitization within the spellchecker's regular expression processing mechanism, creating a pathway for malicious actors to inject and execute arbitrary PHP code on the affected server. The flaw operates through a sophisticated attack vector that leverages the preg_replace function with the /e modifier, which is inherently dangerous due to its ability to execute code contained within regular expressions.
The technical implementation of this vulnerability involves the exploitation of the preg_replace function's /e flag, which was a deprecated but still functional feature in older PHP versions. When the spellchecker processes user input containing specially crafted "complex curly syntax" within regular expressions, the /e modifier causes the PHP interpreter to execute any code embedded within the matched patterns. This creates a classic command injection scenario where attackers can embed PHP code within the regular expression itself, bypassing normal input validation checks and executing arbitrary commands with the privileges of the web server process. The vulnerability is categorized under CWE-94, which specifically addresses the execution of arbitrary code, and aligns with ATT&CK technique T1190 for exploitation of remote services through code injection.
The operational impact of this vulnerability is severe and far-reaching, as it enables complete compromise of the affected DokuWiki installation. Attackers can execute malicious PHP code to establish persistent backdoors, exfiltrate sensitive data, modify content, or use the compromised server for further attacks against other systems. The vulnerability affects not just the spellchecker functionality but potentially the entire web application, as the code execution occurs at the server level where the web application runs. Given that DokuWiki was widely used for collaborative documentation and content management, this vulnerability could have been exploited to compromise numerous websites, wikis, and documentation systems that relied on the affected versions. The exploit requires minimal privileges and can be executed remotely, making it particularly dangerous for systems that are publicly accessible or have weak network security controls.
Mitigation strategies for this vulnerability involve immediate patching of the DokuWiki installation to a version that addresses the security flaw, which would typically include proper input sanitization and the removal of the dangerous /e modifier from regular expression processing. Organizations should also implement web application firewalls to detect and block suspicious regular expression patterns, conduct thorough security audits of all input processing functions, and consider disabling the spellchecker component if it is not essential for operations. Additionally, system administrators should review and harden their PHP configurations to prevent the execution of code within regular expressions, ensuring that the /e modifier is disabled or properly sanitized when used. The vulnerability serves as a critical reminder of the importance of input validation, the dangers of deprecated features, and the necessity of keeping software components updated to protect against known security flaws.