CVE-2015-6733 in MediaWiki
Summary
by MITRE
GeSHi, as used in the SyntaxHighlight_GeSHi extension and MediaWiki before 1.23.10, 1.24.x before 1.24.3, and 1.25.x before 1.25.2, allows remote attackers to cause a denial of service (resource consumption) via unspecified vectors.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 06/14/2022
The vulnerability identified as CVE-2015-6733 affects GeSHi, a syntax highlighting library utilized within the SyntaxHighlight_GeSHi MediaWiki extension. This issue manifests across multiple MediaWiki versions including 1.23.10 and earlier, 1.24.x versions prior to 1.24.3, and 1.25.x versions before 1.25.2. The core problem lies in the improper handling of input data within the GeSHi library, which creates a resource exhaustion condition that can be exploited by remote attackers to disrupt service availability. This vulnerability represents a significant concern for web applications that rely on syntax highlighting functionality, as it directly impacts the availability and performance of the affected systems. The flaw enables attackers to consume excessive system resources through crafted input that triggers inefficient processing within the syntax highlighting engine.
The technical implementation of this vulnerability stems from inadequate input validation and resource management within the GeSHi parsing routines. When MediaWiki processes code snippets through the SyntaxHighlight_GeSHi extension, the underlying GeSHi library fails to properly constrain resource usage during the parsing phase. This allows attackers to submit malicious code samples that cause the parser to consume excessive CPU cycles and memory resources. The vectors for exploitation remain unspecified in the CVE description, but typically involve carefully crafted code blocks that trigger infinite loops, excessive recursion, or other resource-intensive operations within the GeSHi engine. The vulnerability operates at the application level and does not require authentication, making it particularly dangerous as it can be exploited by anyone with access to the affected MediaWiki instance. This behavior aligns with CWE-400, which categorizes resource exhaustion vulnerabilities as those that allow attackers to consume system resources beyond normal operational limits.
The operational impact of CVE-2015-6733 extends beyond simple service disruption to encompass broader system stability and availability concerns. When exploited, this vulnerability can cause the affected MediaWiki instances to become unresponsive, leading to complete denial of service for legitimate users attempting to access or edit content. The resource consumption patterns typically result in system performance degradation that may persist until the affected processes are manually terminated or the system is restarted. Organizations relying on MediaWiki for collaborative content management, documentation, or knowledge base systems face significant operational risks from this vulnerability. The impact is particularly severe in high-traffic environments where multiple users might simultaneously trigger resource exhaustion conditions, potentially affecting the entire system's availability and performance. This vulnerability also creates opportunities for attackers to conduct sustained denial of service attacks against critical infrastructure that depends on MediaWiki platforms.
Mitigation strategies for CVE-2015-6733 primarily focus on applying the official security patches released by the MediaWiki development team. The recommended solution involves upgrading to the patched versions of MediaWiki that contain fixes for the GeSHi library resource consumption issues. Organizations should also implement input validation measures at the application level to limit the complexity and size of code snippets processed through the syntax highlighting functionality. Network-level protections such as rate limiting and resource monitoring can help detect and prevent exploitation attempts. Additionally, implementing proper resource limits and process monitoring on the hosting infrastructure can provide defense-in-depth measures against potential exploitation. Security teams should also consider disabling the SyntaxHighlight_GeSHi extension temporarily if immediate patching is not feasible, while implementing monitoring to detect unusual resource consumption patterns that may indicate exploitation attempts. The remediation process should include thorough testing of patched versions to ensure that legitimate functionality remains intact while addressing the resource exhaustion vulnerability. This approach aligns with ATT&CK technique T1499.004, which addresses denial of service through resource exhaustion, and emphasizes the importance of maintaining up-to-date software versions to prevent exploitation of known vulnerabilities.