CVE-2026-26233
Received Received - Intake
Denial of Service via Unrestricted Login Requests in Mattermost

Publication date: 2026-03-25

Last updated on: 2026-03-26

Assigner: Mattermost, Inc.

Description
Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to rate limit login requests which allows unauthenticated remote attackers to cause denial of service (server crash and restart) via HTTP/2 single packet attack with 100+ parallel login requests.. Mattermost Advisory ID: MMSA-2025-00566
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Meta Information
Published
2026-03-25
Last Modified
2026-03-26
Generated
2026-06-16
AI Q&A
2026-03-25
EPSS Evaluated
2026-06-15
NVD
CVE-2026-26233
EUVD
EUVD-2026-15756
Affected Vendors & Products
Showing 4 associated CPEs
Vendor Product Version / Range
mattermost mattermost_server From 10.11.0 (inc) to 10.11.12 (exc)
mattermost mattermost_server From 11.2.0 (inc) to 11.2.4 (exc)
mattermost mattermost_server From 11.3.0 (inc) to 11.3.2 (exc)
mattermost mattermost_server From 11.4.0 (inc) to 11.4.1 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.
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Executive Summary

This vulnerability exists in certain versions of Mattermost (11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11) where the software fails to rate limit login requests.

Because of this, unauthenticated remote attackers can send a large number of parallel login requests (100 or more) using an HTTP/2 single packet attack, which can cause the server to crash and restart.

Impact Analysis

The primary impact of this vulnerability is a denial of service condition.

An attacker can cause the Mattermost server to crash and restart by sending many parallel login requests without authentication, potentially disrupting service availability.

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