CVE-2018-21259 in Mattermost Server
Summary
by MITRE
An issue was discovered in Mattermost Server before 4.10.1, 4.9.4, and 4.8.2. It allows attackers to cause a denial of service (application hang) via a malformed link in a channel.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability identified as CVE-2018-21259 represents a critical denial of service flaw affecting Mattermost Server versions prior to 4.10.1, 4.9.4, and 4.8.2. This issue stems from inadequate input validation mechanisms within the server's link processing functionality, creating a pathway for malicious actors to disrupt service availability. The vulnerability specifically manifests when the system encounters malformed links within channel communications, leading to application hang conditions that effectively render the service unusable. Such a flaw demonstrates a fundamental weakness in the server's robustness against malformed data inputs, particularly in the context of user-generated content processing.
The technical implementation of this vulnerability involves the server's failure to properly sanitize and validate link structures before processing them within channel environments. When a malicious user submits a malformed link containing specially crafted payloads, the server's parsing mechanisms become overwhelmed or enter infinite loop conditions, causing the application to freeze or become unresponsive. This behavior aligns with CWE-129, which addresses improper validation of input boundaries, and more specifically with CWE-400, concerning resource exhaustion vulnerabilities. The flaw operates at the application layer and affects the server's ability to handle concurrent user requests, as the processing of a single malicious link can block other legitimate operations within the system.
From an operational perspective, this vulnerability presents significant risks to organizations relying on Mattermost for critical communication infrastructure. The denial of service condition can impact entire channels or potentially the entire server instance, depending on the implementation details. Attackers can exploit this weakness to disrupt team communications, potentially causing business disruption and productivity losses. The impact extends beyond simple service interruption as the hanging state may require manual intervention to recover the system, including potential restarts of affected services. This vulnerability particularly affects collaborative environments where real-time communication is essential, making it a serious concern for organizations that depend on continuous availability of their communication platforms.
Organizations should implement immediate mitigations including upgrading to the patched versions of Mattermost Server, specifically versions 4.10.1, 4.9.4, and 4.8.2, which contain proper input validation mechanisms. Additionally, network-level filtering should be implemented to restrict access to known malicious patterns in link formats, though this approach provides only partial protection. The implementation of rate limiting and input sanitization controls can help reduce the impact of such attacks by preventing excessive processing of malformed inputs. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network disruption techniques, and represents a classic example of how improper input validation can be exploited to achieve service disruption. Security teams should also consider implementing monitoring solutions that can detect unusual processing patterns or resource consumption spikes that may indicate exploitation attempts.