CVE-2009-4041 in UseBB
Summary
by MITRE
UseBB 1.0.9 before 1.0.10 allows remote attackers to cause a denial of service (infinite loop) via crafted BBCode tags.
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Analysis
by VulDB Data Team • 08/28/2021
The vulnerability identified as CVE-2009-4041 affects UseBB version 1.0.9 and earlier, representing a critical denial of service flaw that can be exploited remotely by attackers. This issue specifically targets the BBCode parsing functionality within the forum software, where malicious actors can craft specially formatted BBCode tags to trigger an infinite loop condition in the application's processing logic. The vulnerability falls under the category of improper input validation and represents a classic example of a resource exhaustion attack that can bring down the targeted system or service.
The technical implementation of this vulnerability stems from inadequate validation and sanitization of BBCode input within the UseBB forum software. When the application processes malformed BBCode tags, the parsing engine enters an infinite loop due to insufficient boundary checks and recursive processing logic. This flaw demonstrates poor defensive programming practices where the software fails to properly handle malformed input, leading to a condition where the processor continuously executes the same code path without making progress toward completion. The vulnerability can be classified as a CWE-835: Loop with Unreachable Exit Condition, which is a well-documented weakness in software design that directly enables denial of service attacks.
From an operational perspective, this vulnerability presents significant risk to organizations relying on UseBB forum systems, as it allows remote attackers to consume excessive system resources through a simple HTTP request containing crafted BBCode content. The infinite loop causes the web server process to hang indefinitely, potentially leading to complete service unavailability for legitimate users. Attackers can exploit this vulnerability by posting content containing malicious BBCode tags to forums, bulletin boards, or any system component that processes such input. The impact extends beyond simple service disruption as it can affect system availability, user experience, and potentially lead to cascading failures in larger network environments where the vulnerable system serves as a critical component.
The attack vector for this vulnerability is straightforward and requires minimal technical expertise to execute successfully. Remote attackers only need to submit a post or message containing specifically crafted BBCode tags that trigger the parsing loop. This makes the vulnerability particularly dangerous as it can be exploited by anyone with access to the forum system, including unauthenticated users. The vulnerability aligns with ATT&CK technique T1499.004: Endpoint Denial of Service, which focuses on causing service unavailability through resource exhaustion or process interruption. Organizations should consider this vulnerability in their threat modeling exercises as it represents a low-effort, high-impact attack method that can be automated and scaled across multiple targets.
Mitigation strategies for CVE-2009-4041 primarily involve upgrading to UseBB version 1.0.10 or later, which contains the necessary patches to address the infinite loop condition in BBCode parsing. System administrators should also implement input validation measures at multiple layers, including web application firewalls that can detect and block suspicious BBCode patterns before they reach the vulnerable parsing engine. Additional protective measures include implementing resource limits on web server processes, monitoring for unusual CPU utilization patterns, and establishing automated alerting systems to detect potential exploitation attempts. Organizations should also consider implementing rate limiting on user submissions and input sanitization routines that can identify and neutralize potentially malicious BBCode constructs. The vulnerability serves as a reminder of the importance of input validation and proper error handling in web applications, particularly those processing user-generated content that can be leveraged for denial of service attacks.