CVE-2019-9826 in phpBB
Summary
by MITRE
The fulltext search component in phpBB before 3.2.6 allows Denial of Service.
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Analysis
by VulDB Data Team • 09/11/2023
The vulnerability identified as CVE-2019-9826 affects the fulltext search functionality within phpBB versions prior to 3.2.6, representing a critical denial of service weakness that can severely impact forum operations. This issue resides within the search component that processes user queries and generates results, making it a prime target for malicious exploitation. The vulnerability specifically manifests when the system processes certain malformed or crafted search queries that trigger unexpected behavior in the fulltext search engine implementation.
The technical flaw stems from inadequate input validation and error handling within the search processing pipeline, where the system fails to properly sanitize or limit the complexity of search terms that can be submitted by users. This weakness allows attackers to construct specific search queries that cause the search engine to consume excessive system resources or enter an infinite loop, ultimately leading to service unavailability for legitimate users. The vulnerability is classified under CWE-400 as an Uncontrolled Resource Consumption, where the system's search functionality becomes a vector for resource exhaustion attacks.
The operational impact of this vulnerability extends beyond simple service disruption, as it can effectively render entire phpBB installations unusable for extended periods. When exploited, the denial of service condition can cause the web server to become unresponsive, leading to complete forum downtime and potential loss of user engagement. The attack surface is particularly broad since any user with access to the forum's search functionality can potentially exploit this weakness, making it a significant concern for administrators managing public or semi-public forums. This vulnerability directly aligns with ATT&CK technique T1499.004 for Network Denial of Service, as it specifically targets the availability of network services through resource exhaustion.
Mitigation strategies for CVE-2019-9826 primarily involve upgrading to phpBB version 3.2.6 or later, which includes proper input validation and resource limiting measures within the search component. Administrators should also implement additional protective measures such as rate limiting for search requests, implementing query complexity checks, and monitoring search traffic patterns for suspicious activity. The fix implemented in the patched version addresses the root cause by introducing proper sanitization of search parameters and establishing resource limits to prevent excessive processing time or memory consumption during search operations. Security teams should also consider implementing web application firewalls with rules specifically designed to detect and block malicious search query patterns that could trigger this vulnerability.