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VulnerabilityPublished

CVE-2026-19621: Mattermost · Information Exposure

Affects MattermostSource GCVE Database

0

Not known to be exploited · CVSS 6.5 Medium.

Data as of 27 Oct 2026, 22:42 UTC

CVSS 3.1 base score
6.5Medium
How severe the flaw is on the 0–10 CVSS scale.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 16 Oct 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Affected software

ProductAffectedFixed in
Mattermost MattermostAffected
  • 11.7.0 – 11.10.0
4 affected builds
Fixed in–

AI-suggested

Since this is a vulnerability in specific Mattermost versions, users should upgrade to a fixed version once available. Until then, restrict channel membership to trusted users to limit exposure. Monitor the official Mattermost advisory MMSA-2026-00766 for patch releases and apply updates promptly when provided.

Description

Mattermost versions 11.7.0, 11.8.0, 11.9.0, and 11.10.0 contain a vulnerability where action integration secrets are not properly stripped from post payloads before broadcasting post-deletion websocket events and returning thread API responses. This flaw allows authenticated channel members to access sensitive server-side webhook URLs and authentication context from interactive-message posts via the post_deleted websocket event or the threads REST API.

References

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