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CVE-2025-12421

Mattermost Server vulnerability

9.9 CRITICALEPSS 0.34%
  1. Published27 Nov 2025

Description

Mattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to to verify that the token used during the code exchange originates from the same authentication flow, which allows an authenticated user to perform account takeover via a specially crafted email address used when switching authentication methods and sending a request to the /users/login/sso/code-exchange endpoint. The vulnerability requires ExperimentalEnableAuthenticationTransfer to be enabled (default: enabled) and RequireEmailVerification to be disabled (default: disabled).

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredLow
User interactionNone
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Affected products

Mattermost Server≥ 10.11.0 < 10.11.5 · ≥ 10.12.0 < 10.12.2 · ≥ 10.5.0 < 10.5.13 · ≥ 11.0.0 < 11.0.3

Remediation

Fixed in
Mattermost Server≥ 10.11.5

References

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Frequently asked

Is CVE-2025-12421 being actively exploited?

CVE-2025-12421 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.34%.

How severe is CVE-2025-12421?

CVE-2025-12421 has a CVSS 3.1 base score of 9.9, rated critical. EPSS estimates a 0.34% probability of exploitation.

Which products are affected by CVE-2025-12421?

Affected products include Mattermost Server.

How do I fix CVE-2025-12421?

Upgrade affected software to a fixed version, for example Mattermost Server 10.11.5 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2025-12421 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.