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

Severity: medium (CVSS 6.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-26 · updated 2026-06-26
Weakness: CWE-532

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

Mattermost: through 10.18.11; through 11.3.6; through 11.6.5

References

https://mattermost.com/security-updates

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