CVE-2002-1902 in CGIForum
Summary
by MITRE
CGIForum 1.0 through 1.05 allows remote attackers to cause a denial of service (infinite recursion) by creating a message board post that is a child of an outdated parent.
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Analysis
by VulDB Data Team • 09/01/2025
The vulnerability identified as CVE-2002-1902 affects CGIForum versions 1.0 through 1.05, representing a classic denial of service flaw that exploits recursive data structures within message board implementations. This issue manifests when an attacker creates a forum post that references an outdated parent post as its parent, creating a circular reference condition that leads to infinite recursion during post processing. The flaw resides in the forum software's inability to properly validate parent-child relationships in thread hierarchies, allowing malicious users to construct posts that reference themselves or create loops in the posting structure.
From a technical perspective, the vulnerability operates through a recursive traversal mechanism that processes parent-child relationships in forum posts. When a post is created with an outdated parent reference, the system attempts to resolve the thread hierarchy by following parent references recursively. This recursive processing continues indefinitely when the parent reference points to a post that either references back to the current post or to a chain that eventually loops back to the starting point. The system lacks proper cycle detection or recursion depth limiting mechanisms, causing the processing to consume excessive CPU resources and memory until system resources are exhausted.
The operational impact of this vulnerability extends beyond simple service disruption, as it represents a fundamental flaw in data validation and thread management within web-based forum applications. Attackers can exploit this weakness to render entire forum systems unavailable to legitimate users, potentially affecting thousands of forum participants simultaneously. The vulnerability is particularly dangerous because it requires minimal technical expertise to exploit, making it attractive to attackers seeking to disrupt online communities or web services. The infinite recursion consumes system resources rapidly, leading to complete service unavailability rather than partial degradation.
This vulnerability aligns with CWE-674, which describes "Uncontrolled Recursion" as a weakness that occurs when a program fails to detect or limit recursive calls that can lead to stack overflow or resource exhaustion. The flaw also corresponds to ATT&CK technique T1499.004, which covers "Endpoint Denial of Service" through resource exhaustion attacks. The vulnerability demonstrates poor input validation and insufficient boundary checking in recursive data structures, which are common patterns in legacy web applications that were not designed with robust error handling in mind. Organizations should implement recursion depth limits, cycle detection algorithms, and proper parent-child relationship validation to prevent similar issues in forum and discussion board implementations.
Mitigation strategies should include implementing maximum recursion depth limits in the forum software, adding cycle detection mechanisms that identify circular parent-child references, and enforcing strict validation of parent post references during post creation. System administrators should also consider implementing rate limiting and resource monitoring to detect unusual processing patterns that might indicate exploitation attempts. The vulnerability highlights the importance of defensive programming practices and proper input sanitization in web applications, particularly those handling hierarchical data structures. Regular security audits and code reviews focusing on recursive data processing and thread management can help identify and prevent similar issues in other legacy systems.