CVE-2008-5185 in geshi
Summary
by MITRE
The highlighting functionality in geshi.php in GeSHi before 1.0.8 allows remote attackers to cause a denial of service (infinite loop) via an XML sequence containing an opening delimiter without a closing delimiter, as demonstrated using "<".
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 01/11/2025
The vulnerability identified as CVE-2008-5185 affects the GeSHi library, a popular syntax highlighting tool used across numerous web applications and content management systems. This issue resides within the geshi.php file and represents a classic example of improper input validation that can lead to resource exhaustion. The flaw specifically targets the library's ability to process XML sequences, where the absence of proper delimiter matching creates a condition that can be exploited to trigger infinite loops during parsing operations. The vulnerability demonstrates how seemingly benign input patterns can be weaponized to disrupt service availability, making it a significant concern for systems relying on GeSHi for code display functionality.
The technical root cause of this vulnerability stems from inadequate state management within the GeSHi highlighting engine's XML parsing routines. When processing input containing an opening delimiter such as "<" without a corresponding closing delimiter, the parser enters an infinite loop attempting to find the matching closing tag. This condition occurs because the parsing algorithm lacks proper bounds checking and termination conditions for unbalanced delimiters. The flaw is classified under CWE-835, which addresses the issue of infinite loops in software, and represents a specific case of improper input validation where the system fails to handle malformed input gracefully. The vulnerability operates at the application layer and can be exploited through any mechanism that allows user input to be processed by the GeSHi library, including web forms, API endpoints, or file upload handlers.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be leveraged to consume excessive system resources and potentially disrupt legitimate service operations. Attackers can craft malicious payloads that cause the target system to enter continuous processing loops, consuming CPU cycles and memory resources until the system becomes unresponsive or crashes. This type of attack falls under the ATT&CK technique T1499.004, which describes denial of service through resource exhaustion. The vulnerability affects any system using GeSHi versions prior to 1.0.8, making it particularly dangerous as it could be present in numerous web applications, content management systems, and development tools that rely on this library for code highlighting functionality. The impact is amplified in environments where multiple users can submit content or where the library is used in high-traffic scenarios.
Mitigation strategies for CVE-2008-5185 primarily involve upgrading to GeSHi version 1.0.8 or later, which contains the necessary fixes to properly handle unbalanced delimiters and prevent infinite loop conditions. Organizations should also implement input sanitization measures at the application level to validate and filter user-supplied content before it reaches the GeSHi processing engine. Additional protective measures include implementing resource limits and timeouts for parsing operations, as well as monitoring for unusual CPU usage patterns that might indicate exploitation attempts. The fix implemented in version 1.0.8 typically involves adding proper bounds checking and termination conditions to the XML parsing routines, ensuring that unmatched delimiters do not cause the parser to enter indefinite loops. Security teams should also consider implementing web application firewalls that can detect and block malicious input patterns associated with this vulnerability, particularly in environments where upgrading the library is not immediately feasible.