Vulnerability · Published Jun 26, 2026 · Assigned by Mattermost

CVE-2026-9699Mattermost Agents plugin logs unsanitized OpenAI API keys on authentication errors

Medium 6.8

In plain English

A medium-severity sensitive data in logs in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 40% of all known vulnerabilities).

Severity (CVSS 3.1)6.8Medium

Exploit odds (30 days)0.5%top 60.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Mattermost Plugins versions <=11.6 10.18.11 11.3.6 11.6.5.0 fail to sanitize error responses from the OpenAI API before logging, which allows a user with access to server logs or support packets to obtain a valid or partially reconstructable OpenAI API key via inspection of mattermost.log entries generated during authentication failures. Mattermost Advisory ID: MMSA-2026-00609

Affected products (as reported)

Vendor	Product	Versions
Mattermost	Mattermost	0 – through 10.18.110 – through 11.3.60 – through 11.6.5

Weakness: CWE-532 · Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N

References

MMSA-2026-00609 vendor-advisory