# CVE-2026-19621: Mattermost information disclosure in post deletion events

Source: https://junglewise.ai/threats/cve-2026-19621-mattermost-versions-11-10-x-11-10-0-11-7-x-11-7-9-11-9-x-11-9-1  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-16. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-19621 · Severity: medium · CVSS 6.5 · Published 2026-10-16

Mattermost, a team collaboration platform, fails to remove sensitive webhook credentials from messages when posts are deleted. An authenticated user with channel access can intercept these credentials through WebSocket events or API responses, gaining unauthorized access to external integrations and potentially compromising connected systems.

Technologies: [Mattermost Server](https://junglewise.ai/threats/technologies/server-public). Vendors: [Mattermost](https://junglewise.ai/threats/vendors/mattermost).

## Quick answers

**Is CVE-2026-19621 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-19621 being exploited in the wild.

**How severe is CVE-2026-19621?** Medium severity, with a CVSS score of 6.5, published 16 October 2026.

**Which products and versions are affected?** Mattermost Server 11.7.x <= 11.7.9, 11.8.x <= 11.8.5, 11.9.x <= 11.9.1, 11.10.x <= 11.10.0.

**Is there a fix for CVE-2026-19621?** Yes: fixed in Mattermost Server 11.7.10, 11.8.6, 11.9.2, 11.10.1. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-19621 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-19621?** Check whether you run Mattermost Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in Mattermost Server 11.7.10, 11.8.6, 11.9.2, 11.10.1

## Technical details

The vulnerability allows authenticated channel members to retrieve server-side webhook URLs and authentication context from interactive-message action integrations. Sensitive data is not stripped from post_deleted WebSocket events and thread REST API responses before broadcast, exposing action integration secrets to users who should not have access to them.

## Affected products

- Mattermost Mattermost Server 11.7.x <= 11.7.9, 11.8.x <= 11.8.5, 11.9.x <= 11.9.1, 11.10.x <= 11.10.0

## Timeline

- 2026-10-16: disclosed

## References

- [https://mattermost.com/security-updates](https://mattermost.com/security-updates)

## Related threats

- [Mattermost CSRF via Agents plugin mention reminder validation](https://junglewise.ai/threats/cve-2026-93851-mattermost-versions-11-9-x-11-9-1-11-8-x-11-8-5-11-7-x-11-7-10)
- [Mattermost denial of service via PDF text extraction memory exhaustion](https://junglewise.ai/threats/cve-2026-93850-mattermost-versions-11-9-x-11-9-1-11-8-x-11-8-5-11-7-x-11-7-10-11)
- [Mattermost denial of service in WebSocket msgpack decoder](https://junglewise.ai/threats/cve-2026-93849-mattermost-versions-11-9-x-11-9-1-11-8-x-11-8-5-11-7-x-11-7-10-11)
- [Mattermost authentication token leak in server logs](https://junglewise.ai/threats/cve-2026-19600-mattermost-versions-11-9-x-11-9-1-11-8-x-11-8-5-11-7-x-11-7-10-11)
- [Mattermost authentication bypass in OAuth account takeover](https://junglewise.ai/threats/cve-2026-19076-mattermost-versions-11-10-x-11-10-0-11-7-x-11-7-9-11-9-x-11-9-1)