CVE-2026-12882
Received Received - Intake

Denial of Service in Mattermost via Malformed Markdown Autolinks

Publication date: 2026-09-14

Last updated on: 2026-09-14

Assigner: Mattermost, Inc.

Description
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to parse Markdown autolinks with unmatched trailing closing parentheses in linear time, which allows an authenticated user with permission to create posts to cause excessive server CPU consumption and degrade availability for other users via specially crafted post or message attachment content. Mattermost Advisory ID: MMSA-2026-00703

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Meta Information

Published
2026-09-14
Last Modified
2026-09-14
Generated
2026-09-14
AI Q&A
2026-09-14
EPSS Evaluated
N/A
NVD
CVE-2026-12882
EUVD
EUVD-2026-77363

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
mattermost mattermost to 11.9.0 (inc)
mattermost mattermost to 11.8.4 (inc)
mattermost mattermost to 11.7.7 (inc)
mattermost mattermost to 10.11.22 (inc)

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-407 An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.

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Executive Summary

Mattermost versions between 11.9.0 and older, 11.8.4 and older, 11.7.7 and older, and 10.11.22 and older fail to properly handle Markdown autolinks with unmatched trailing closing parentheses. This causes the server to consume excessive CPU resources when processing crafted post or message content, leading to degraded performance for all users.

Impact Analysis

An authenticated user with post creation permissions could exploit this to slow down or crash the Mattermost server, affecting all users by making the system unresponsive or unavailable during peak usage.

Mitigation Strategies

Upgrade Mattermost to a version that fixes this issue. Specifically, update to versions beyond 11.9.0, 11.8.4, 11.7.7, or 10.11.22 depending on your current installation. This addresses the Markdown autolink parsing flaw causing CPU exhaustion.

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