CVE-2023-5876 in Mattermost
Summary
by MITRE • 11/02/2023
Mattermost fails to properly validate a RegExp built off the server URL path, allowing an attacker in control of an enrolled server to mount a Denial Of Service.
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Analysis
by VulDB Data Team • 11/30/2023
The vulnerability identified as CVE-2023-5876 affects the Mattermost collaborative platform, specifically targeting its server URL path validation mechanism. This issue arises from improper handling of regular expression construction based on server URL paths, creating a potential vector for denial of service attacks. The flaw exists within the server-side processing logic where user-controllable input is directly incorporated into regular expression patterns without adequate sanitization or validation. This type of vulnerability falls under the category of improper input validation as classified by CWE-20, which represents one of the most common software security weaknesses in the industry.
The technical implementation of this vulnerability stems from the way Mattermost constructs regular expressions using server URL path components that may be manipulated by attackers. When an enrolled server is compromised or when an attacker gains control over a server that has been registered with Mattermost, they can exploit this weakness by crafting malicious URL paths that result in malformed or excessively complex regular expressions. The improper validation allows these crafted inputs to be directly processed into regular expression objects, potentially leading to catastrophic backtracking or resource exhaustion during pattern matching operations. This type of vulnerability is particularly dangerous in server environments where regular expressions are used for URL routing, access control, or content filtering, as it can consume significant system resources and render the service unavailable to legitimate users.
The operational impact of CVE-2023-5876 extends beyond simple service disruption, as it represents a potential escalation path for attackers who have already gained access to an enrolled server. The denial of service condition can be sustained and may require system restarts or manual intervention to restore normal operations. Organizations using Mattermost platforms face risks of extended downtime, degraded service quality, and potential data access issues that could affect collaboration and communication workflows. The vulnerability also demonstrates poor defensive programming practices where input validation is insufficient to prevent malicious inputs from being processed through critical system components, aligning with ATT&CK technique T1499.004 for network denial of service attacks. This weakness is particularly concerning in enterprise environments where Mattermost is used for critical communication and collaboration purposes, as the service disruption can impact productivity and business continuity.
Mitigation strategies for CVE-2023-5876 should focus on implementing robust input validation and sanitization mechanisms for URL path components before they are used to construct regular expressions. Organizations should ensure that all user-controllable inputs undergo proper validation, including length restrictions, character set validation, and pattern matching to prevent malicious inputs from being processed. The implementation of regular expression compilation with time and resource limits can help prevent catastrophic backtracking scenarios, while also ensuring that regular expression patterns are built using safe, static inputs rather than user-controllable data. Additionally, organizations should consider implementing rate limiting and monitoring mechanisms to detect unusual patterns of regular expression usage that may indicate exploitation attempts. The fix should involve proper separation of concerns in the codebase where URL path processing and regular expression construction are decoupled, with validation occurring at multiple levels to ensure that malicious inputs cannot reach the core regular expression engine. This vulnerability highlights the importance of following secure coding practices and implementing defense-in-depth strategies to protect against both known and unknown threats in collaborative software platforms.