CVE-2026-4339

mediumpriority · track · 0EPSS 0.001 · 3 %ileDEEUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

0.14% (3rd) EPSS

CVSS 6.5 · medium

Is it mine?

22 products

Check your exposure

Who says so?

4 sources

cnnvd · enisa_euvd · cert_bund · nvd

EPSS · scored 2026-10-27

Mattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery (SSRF) and exfiltrate data from internal network services via supplying internal URLs as file attachments in post creation requests.. Mattermost Advisory ID: MMSA-2026-00635

cvss

Technical severity, 0–10. One row per scoring source.

6.5

010

base score 0–10 · higher = more severe · hover a vector to decode

v3.16.5mediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:Nsecondary · ENISA EU

v3.16.5mediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:Nsecondary · responsibledisclosure@mattermost.comexploitability 2 · impact 4

v3.16mediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N/E:Usecondary · CVSS-BT (t0sche)

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Trackcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-918US

affected products (22)

Products and version ranges known to be affected.

Mattermost Mattermost Plugins <10.11.19all versionscert_bundDE
Mattermost Mattermost Plugins <11.5.7all versionscert_bundDE
Mattermost Mattermost Plugins <11.6.4all versionscert_bundDE
Mattermost Mattermost Plugins <11.7.0all versionscert_bundDE
Mattermost Mattermost Server <10.11.19all versionscert_bundDE
Mattermost Mattermost Server <11.5.7all versionscert_bundDE
Mattermost Mattermost Server <11.6.4all versionscert_bundDE
Mattermost Mattermost Server <11.7.0all versionscert_bundDE
Mattermost Mattermost≤ Plugins <11.7.0cert_bundDE
Mattermost Mattermost≤ Plugins <10.11.19cert_bundDE
Mattermost Mattermost≤ Plugins <11.5.7cert_bundDE
Mattermost Mattermost≤ Plugins <11.6.4cert_bundDE
Mattermost Mattermost≤ Server <10.11.19cert_bundDE
Mattermost Mattermost≤ Server <11.5.7cert_bundDE
Mattermost Mattermost≤ Server <11.6.4cert_bundDE
Mattermost Mattermost≤ Server <11.7.0cert_bundDE
Mattermost Mattermost≤ 10.11.0 ≤10.11.18enisa_euvdEU
Mattermost Mattermost≤ 11.5.0 ≤11.5.6enisa_euvdEU
Mattermost Mattermost≤ 11.6.0 ≤11.6.3enisa_euvdEU
mattermost mattermost server10.11.0 → 10.11.19nvdUScpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

showing 20 of 22

advisories (1)

Vendor and ecosystem advisories describing this.

WID-SEC-W-2026-1705Mattermost Server und Plugins: Mehrere Schwachstellen ermöglichen nicht spezifizierten AngriffDeutsch2026-05-27csaf · cert_bundDE
Ein Angreifer kann mehrere Schwachstellen in Mattermost Server und Plugins ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen.

also known as (3)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd cert_bund nvd NVD CVE.org MITRE

published 2026-06-26modified 2026-06-29

references (3)

External citations — patches, advisories, analysis.

scry

Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.

Free scan