CVE-2026-19621 Mattermost leaks interactive-message integration secrets to non-admin users via post-deletion events and thread reads
Authenticated users can obtain sensitive webhook URLs and authentication secrets from interactive messages via post deletion events or thread APIs.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-19621?
CVE-2026-19621 is a medium-severity vulnerability in Mattermost Mattermost Server, published on 16 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to strip action integration secrets from post payloads before broadcasting post-deletion web socket events and returning thread API responses, which allows an authenticated channel member to obtain server-side webhook URLs and authentication context from interactive-message posts via the post_deleted websocket event or the threads REST API.. Mattermost Advisory ID: MMSA-2026-00766
Weakness: CWE-200
Which versions are affected by CVE-2026-19621?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-19621?
No fix has been published for CVE-2026-19621 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-19621 being exploited?
There is no known exploitation of CVE-2026-19621 in the wild and no public exploit code.
Other vulnerabilities in Mattermost Mattermost Server
- CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers
- CVE-2025-12421 Account Takeover via Code Exchange Endpoint
- CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User
- CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards
- CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive
Sources
Also known as GHSA-9mh4-36gv-g7wx.