CVE-2026-96259

Mattermost server-side request forgery via OAuth endpoints configurable by a System Administrator

State: Published
Severity: 5.5 Medium
Published: Sep 22, 2026
Updated: Sep 23, 2026
Reserved: Sep 22, 2026

Description

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to apply the internal-connection filter to OAuth endpoint requests, which allows a System Administrator to make the server issue requests to internal network addresses and read the responses via the configured OAuth token and userinfo endpoints.. Mattermost Advisory ID: MMSA-2026-00776

Scores

CVSS	Score	Vector	Source
3.1	5.5 Medium	CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N	Mattermost

Weaknesses

CWE-918 Server-Side Request Forgery (SSRF)

Affected Products

Product	Versions
MattermostMattermost	11.9.0 through 11.9.1Affected 11.8.0 through 11.8.5Affected 11.7.0 through 11.7.10Affected 11.10.0 through 11.10.1Affected 11.11.0Not affected 11.9.2Not affected 11.8.6Not affected 11.7.11Not affected 11.10.2Not affected

References

MMSA-2026-00776vendor-advisory

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