CVE-2026-19621: Mattermost · Information Exposure
Affects MattermostSource GCVE Database
Not known to be exploited · CVSS 6.5 Medium.
Data as of 27 Oct 2026, 22:42 UTC
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:NExploitation evidence
Disclosed: evidence found.
CVE published 16 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| Mattermost Mattermost | Affected
| 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.