CVE-2015-6736 in Quiz Extension
Summary
by MITRE
The Quiz extension for MediaWiki allows remote attackers to cause a denial of service via regex metacharacters in a regular expression.
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Analysis
by VulDB Data Team • 06/14/2022
The CVE-2015-6736 vulnerability affects the Quiz extension for MediaWiki, a widely used wiki software platform that powers numerous websites including Wikipedia. This particular flaw represents a classic regular expression denial of service (REDoS) vulnerability that exploits the way the extension processes user input through regular expressions. The vulnerability arises when malicious users submit quiz questions or answers containing specially crafted regex metacharacters that cause the regular expression engine to consume excessive computational resources during pattern matching operations.
The technical implementation of this vulnerability stems from the Quiz extension's inadequate input validation and sanitization mechanisms when handling user-provided content. When users create quiz questions or define answer patterns, the system employs regular expressions to validate responses and match user inputs against expected answers. However, the extension fails to properly escape or sanitize special regex metacharacters such as asterisks, plus signs, or nested quantifiers that can cause catastrophic backtracking in regular expression engines. This occurs when the regex engine attempts to match patterns that would require exponential time complexity, effectively allowing attackers to craft inputs that can cause the system to hang or crash.
From an operational perspective, this vulnerability presents a significant risk to MediaWiki installations that host quiz content, particularly those with public user contributions or community-driven quiz creation features. Attackers can exploit this weakness by submitting malicious quiz questions or answer patterns that trigger the regex engine to enter infinite loops or consume excessive CPU resources, leading to complete denial of service for legitimate users. The impact extends beyond simple service disruption as it can affect the entire MediaWiki platform, potentially causing cascading failures in related services that depend on the wiki infrastructure. Organizations using this extension may experience increased server load, application unresponsiveness, and potential resource exhaustion that could affect other services running on the same infrastructure.
The vulnerability aligns with CWE-1321, which specifically addresses regular expression denial of service flaws in software systems. According to ATT&CK framework category T1499, this represents a denial of service attack technique that can be executed through input manipulation. Organizations should implement immediate mitigations including input validation and sanitization of all user-provided content before it is processed by regex engines, implementing timeouts for regex operations, and applying the latest security patches provided by the MediaWiki community. Additionally, deploying web application firewalls with regex-based detection capabilities can help identify and block malicious inputs before they reach the vulnerable extension. System administrators should also consider implementing rate limiting and monitoring mechanisms to detect unusual patterns of resource consumption that may indicate exploitation attempts. The remediation process requires updating the Quiz extension to a patched version and conducting thorough input validation across all user-facing components that process regular expressions to prevent similar vulnerabilities from occurring in other parts of the MediaWiki ecosystem.