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EUVD-2025-199827Published

Mattermost versions 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12, 11.0.x <= 11.0.3 fail to properly validate OAuth state tokens during OpenID Connect authentication which allows an authenticated attacker with team creation priv…

Exact source revision recorded 5 Nov 2026 01:00:17 UTC. It does not establish the source's current position. Latest evidence.

Recorded JSON

euvd · EUVD-2025-199827

Published

Mattermost versions 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12, 11.0.x <= 11.0.3 fail to properly validate OAuth state tokens during OpenID Connect authentication which allows an authenticated attacker with team creation privileges to take over a user account via manipulation of authentication data during the OAuth completion flow. This requires email verification to be disabled (default: disabled), OAuth/OpenID Connect to be enabled, and the attacker to control two users in the SSO system with one of them never having logged into Mattermost.

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Nov 27, 2025, 3:55:44 PM

dateUpdated: Feb 26, 2026, 4:07:27 PM

1 related source bulletins · separate from aliases

NCSC-2025-0378: Kwetsbaarheden verholpen in Mattermost

CVE-2025-12421 · CVE-2025-12419

Source published
Nov 27, 2025, 3:55:44 PM (timezone not stated)
Source modified
Feb 26, 2026, 4:07:27 PM (timezone not stated)
Observed here
5 Nov 2026 01:00:17 UTC
Source terms
ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 9.9 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

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Sources read 8 Nov 23:10 UTC · 275 of 275 readable · 273 fully read · documentation 469/469 current

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