Mattermost server-side request forgery via OAuth endpoints configurable by a System Administrator (CVE-2026-96259) | HOL Guard CVE

Medium · CVSS 5.5CVE-2026-96259

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

Answer in brief

CVE-2026-96259 records a Medium severity (CVSS 5.5) vulnerability in Mattermost server-side request forgery via OAuth endpoints configurable by a System Administrator. The current sources do not mark it as known exploited. The current feed maps Mattermost/Mattermost (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 22, 2026Updated Sep 22, 2026Source checked Sep 22, 2026First seen by HOL Sep 22, 2026Material review Sep 22, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 5.5
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

CVSS is 5.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Mattermost/Mattermost (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Mattermost/Mattermostgeneric	>=11.9.0 <=11.9.1 \|\| >=11.8.0 <=11.8.5 \|\| >=11.7.0 <=11.7.10 \|\| >=11.10.0 <=11.10.1	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Mattermost/Mattermost.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 22, 2026

Sources and claim methodology

Source referencemattermost.com

Upstream source 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

Quoted source text, attributed separately from HOL analysis.