CVE-2002-0533 in phpBB
Summary
by MITRE
phpBB 1.4.4 and earlier with BBcode allows remote attackers to cause a denial of service (CPU consumption) and corrupt the database via null \0 characters within [code] tags.
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Analysis
by VulDB Data Team • 06/04/2019
The vulnerability identified as CVE-2002-0533 represents a critical security flaw in phpBB versions 1.4.4 and earlier that specifically targets the BBcode parsing functionality within the forum software. This issue manifests when malicious actors insert null characters within code tags, creating a condition that triggers excessive cpu consumption and potential database corruption. The vulnerability operates at the application layer and affects the core message parsing mechanism that processes user-generated content. phpBB, being a widely deployed open source forum solution, makes this vulnerability particularly dangerous as it can be exploited by remote attackers without requiring authentication or elevated privileges. The flaw demonstrates a classic example of improper input validation and handling of special characters within markup processing systems.
The technical root cause of this vulnerability lies in the insufficient sanitization and processing of null characters within BBcode [code] tags during message parsing operations. When phpBB encounters null characters within these specific tag contexts, the parsing algorithm enters an infinite loop or consumes excessive cpu cycles due to flawed string handling routines. This occurs because the software does not properly validate or escape null byte sequences before processing them through the code formatting engine. The vulnerability is categorized under CWE-129 as an insufficient input validation, specifically manifesting as improper handling of special characters in markup processing. The improper input validation creates a condition where malformed data can cause the application to consume resources indefinitely while attempting to process the malformed content.
The operational impact of this vulnerability extends beyond simple denial of service to include potential data integrity issues within the affected database. Remote attackers can leverage this flaw to consume significant cpu resources, potentially causing system instability or complete service unavailability for legitimate users. The database corruption aspect arises from the parsing errors that can lead to malformed data entries or inconsistent state conditions within the forum's data storage. This vulnerability directly impacts the availability and integrity of forum services, making it particularly dangerous in production environments where continuous uptime is critical. The attack vector requires no special privileges and can be executed through standard web browser interactions, making it highly exploitable across various network configurations. Organizations relying on phpBB for community forums, support systems, or collaborative platforms face significant risk from this vulnerability.
Mitigation strategies for CVE-2002-0533 should prioritize immediate software updates to phpBB versions that address this specific parsing vulnerability. System administrators should implement input filtering mechanisms that sanitize or reject null characters within BBcode contexts before they reach the parsing engine. Network-based solutions such as web application firewalls can be configured to detect and block requests containing null byte sequences within code tags. Additionally, implementing rate limiting and resource monitoring can help detect and prevent exploitation attempts before they cause significant damage. The vulnerability highlights the importance of proper input validation and error handling in web applications, aligning with ATT&CK technique T1499 for resource hijacking and T1566 for credential harvesting through application layer attacks. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security updates and maintain compliance with security best practices outlined in industry standards such as NIST SP 800-53 and ISO 27001.