CVE-2026-2456 in service
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 Mattermost fails to limit the size of responses from integration action endpoints, which allows an authenticated attacker to cause server memory exhaustion and denial of service via a malicious integration server that returns an arbitrarily large response when a user clicks an interactive message button.. Mattermost Advisory ID: MMSA-2026-00571
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Analysis
by VulDB Data Team • 03/20/2026
This vulnerability in Mattermost represents a critical denial of service weakness that stems from inadequate input validation within the integration action processing pipeline. The flaw exists in versions 11.3.0 and earlier, 11.2.2 and earlier, and 10.11.10 and earlier, where the system fails to enforce size limitations on responses received from external integration endpoints. When users interact with clickable buttons in interactive messages, the system retrieves data from configured integration servers without implementing proper response size constraints, creating a potential memory exhaustion scenario. This vulnerability specifically affects the integration action endpoint handling mechanism that processes user interactions with interactive message elements.
The technical implementation of this vulnerability allows an authenticated attacker to exploit the lack of response size validation by configuring a malicious integration server that deliberately returns excessively large responses. When a user clicks an interactive message button, the Mattermost server attempts to process the entire response from the integration endpoint without any size limitations, leading to progressive memory consumption until system resources are exhausted. This memory exhaustion ultimately results in a denial of service condition that affects legitimate users and potentially impacts the entire server functionality. The vulnerability operates at the application layer and specifically targets the server-side processing of integration responses within the messaging platform's interactive message framework.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the overall stability and availability of Mattermost instances. Attackers can leverage this weakness to consume server memory resources rapidly, causing the system to become unresponsive to legitimate requests or even crash entirely. This affects not only individual user experiences but also organizational communication workflows that depend on the messaging platform for collaboration. The vulnerability is particularly concerning in enterprise environments where Mattermost serves as a critical communication infrastructure, as it can be exploited to disrupt business operations and communication channels.
Organizations should implement immediate mitigations including updating to patched versions of Mattermost where available, implementing custom response size limits at the integration endpoint level, and monitoring for unusual memory consumption patterns. The vulnerability aligns with CWE-770, which addresses the allocation of resources without proper limits or throttling mechanisms. From an attack perspective, this vulnerability maps to ATT&CK technique T1499.004 for network denial of service and T1078.004 for valid accounts, as it requires authentication but can be exploited to cause system-wide disruption. Administrative users should also consider implementing network-level rate limiting and size constraints on integration endpoints to provide additional defense in depth.