# CVE-2026-19541: Mattermost OAuth connection secret exposure via validation bypass

Source: https://junglewise.ai/threats/cve-2026-19541-mattermost-versions-11-9-x-11-9-1-11-8-x-11-8-5-11-7-x-11-7-10-11  
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-2026-19541 · Severity: medium · CVSS 6.5 · Published 2026-10-16

Mattermost is a team collaboration platform that manages OAuth connections to third-party services. A flaw in versions 11.7 through 11.10 allows authenticated users with permission to manage OAuth connections to extract the stored client secret by redirecting the validation flow to an attacker-controlled server. This could enable an attacker to impersonate the OAuth application or access data on connected services.

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

## Quick answers

**Is CVE-2026-19541 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-19541 being exploited in the wild.

**How severe is CVE-2026-19541?** Medium severity, with a CVSS score of 6.5, published 16 October 2026.

**Which products and versions are affected?** Mattermost Server 11.7 through 11.7.10, 11.8 through 11.8.5, 11.9 through 11.9.1, 11.10 through 11.10.1.

**Is there a fix for CVE-2026-19541?** Yes: fixed in Mattermost Server 11.7.11, 11.8.6, 11.9.2, 11.10.2. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-19541 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-19541?** 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 11.7.11, 11.8.6, 11.9.2, 11.10.2

## Technical details

The vulnerability is an information disclosure issue in outgoing OAuth connection validation that fails to re-authenticate or re-validate the client secret before sending it to the token URL during validation. An authenticated administrator can exploit this by modifying the token URL to point to an attacker-controlled endpoint, causing the client secret to be transmitted in plaintext. No user interaction beyond the initial validation trigger is required.

## Affected products

- Mattermost Mattermost Server 11.7 through 11.7.10, 11.8 through 11.8.5, 11.9 through 11.9.1, 11.10 through 11.10.1

## 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 information disclosure in post deletion events](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)
- [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)