CVE-2026-2454 in Mattermost
Summary
by MITRE • 03/16/2026
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to handle incorrectly reported array lengths which allows malicious user to cause OOM errors and crash the server via sending corrupted msgpack frames within websocket messages to calls plugin. Mattermost Advisory ID: MMSA-2025-00537
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Analysis
by VulDB Data Team • 03/21/2026
The vulnerability identified as CVE-2026-2454 represents a critical memory management flaw within the Mattermost communication platform that affects multiple version branches including 11.3.0, 11.2.2, and 10.11.10. This issue specifically targets the calls plugin component and exploits improper handling of array length reporting within msgpack frame processing. The vulnerability stems from the application's failure to validate array length specifications when processing websocket messages, creating a pathway for malicious actors to manipulate memory allocation behavior. The flaw operates at the protocol level where msgpack data structures are parsed, making it particularly dangerous as it can be triggered through normal communication channels without requiring elevated privileges or specialized access. The affected versions demonstrate a consistent pattern of inadequate input validation that allows attackers to craft malicious payloads that appear legitimate but contain malformed array length indicators.
The technical execution of this vulnerability involves sending specially crafted websocket messages containing corrupted msgpack frames to the calls plugin endpoint. When the server processes these malformed messages, it attempts to allocate memory based on the incorrectly reported array lengths, leading to excessive memory consumption patterns that ultimately result in out-of-memory conditions. This memory exhaustion occurs during the deserialization process where the system allocates resources based on deceptive array size indicators rather than actual data content. The vulnerability manifests as a denial-of-service condition that can crash the Mattermost server instance, effectively disrupting communication services for all users within the affected environment. The exploitation mechanism aligns with common software security weaknesses documented under CWE-129 and CWE-704, specifically addressing improper input validation and memory allocation errors that can be leveraged for resource exhaustion attacks.
The operational impact of CVE-2026-2454 extends beyond simple service disruption to potentially compromise the availability and reliability of critical communication infrastructure within organizations relying on Mattermost for team collaboration. Server crashes resulting from this vulnerability can lead to extended downtime periods that affect productivity and business continuity, particularly in environments where real-time communication is essential. The attack vector through websocket messages means that any user with access to the calls plugin functionality can potentially trigger the vulnerability, making it a significant concern for organizations with broad user access policies. The memory consumption pattern characteristic of this flaw can also lead to system instability, potentially causing cascading failures in environments where multiple services share system resources. This vulnerability directly impacts the availability aspect of the CIA triad and can be categorized under ATT&CK technique T1499.004 for network denial of service attacks, representing a sophisticated approach to service disruption through memory manipulation.
Organizations should prioritize immediate remediation through version updates to Mattermost releases that address this specific memory handling flaw, as the vulnerability affects multiple stable release branches. The recommended mitigation strategy involves implementing network-level controls to monitor and filter websocket traffic for suspicious msgpack frame patterns, though this approach provides only partial protection given the vulnerability's nature. System administrators should also consider implementing memory monitoring solutions that can detect unusual allocation patterns and automatically trigger alerts when memory consumption exceeds normal operational thresholds. Additionally, organizations should conduct comprehensive testing of their Mattermost deployments to identify any custom configurations or plugins that might interact with the affected calls plugin functionality. The vulnerability's classification as a memory exhaustion issue underscores the importance of implementing robust resource management policies and ensuring adequate system capacity to handle unexpected memory allocation patterns. Security teams should also consider implementing network segmentation strategies to limit potential attack surface and reduce the impact of successful exploitation attempts.