Riskcovery

CVE-2026-6850

Crafted message attachment causes client-side denial of service via markdown parser regex backtracking in Mattermost

State
Published
Severity
6.5 Medium
Published
Jul 13, 2026
Updated
Jul 13, 2026
Reserved
Apr 22, 2026

Read the record on cve.org

Description

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate the length and content of message attachment field values, which allows an authenticated attacker to cause a denial of service for all users in a channel via a post containing a specially crafted payload that triggers catastrophic backtracking in the client-side markdown parser.. Mattermost Advisory ID: MMSA-2026-00658

Scores

CVSSScoreVectorSource
3.16.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HMattermost

Weaknesses

  • CWE-1333 Inefficient Regular Expression Complexity

Affected Products

ProductVersions
MattermostMattermost
  • 11.7.0 through 11.7.2Affected
  • 11.6.0 through 11.6.4Affected
  • 10.11.0 through 10.11.19Affected
  • 11.8.0Not affected
  • 11.7.3Not affected
  • 11.6.5Not affected
  • 10.11.20Not affected

References

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