CVE-2025-12421

Q: How do I fix CVE-2025-12421?

Upgrade mattermost server to 11.0.3 or later.

Q: Is CVE-2025-12421 being actively exploited?

Not that we know of. CVE-2025-12421 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.35% is the estimated probability that it will be exploited in the next 30 days. That is higher than 27% of all scored CVEs.

Q: How severe is CVE-2025-12421?

CVE-2025-12421 has a CVSS v3 base score of 9.9, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2025-12421 affect?

Published advisories record a fix for mattermost server (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

CRITICAL

9.9

CVSS v3

NVD

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).

CWE-303

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 11.0.0, < 11.0.3Fixed in:11.0.3CVE-2025-12421derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

ScopeChanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Exploit Intelligence

0.35%probability of exploitation in 30 days

27thpercentile

Low risk: more likely to be exploited than 27% of all known CVEs.

References

Vendor Advisory1

mattermost.com

Related Vulnerabilities

Other CWE-303 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-7593	Critical	9.8	100%	KEV	-
CVE-2023-29357	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2020-8863	High	8.8	77%	-	-
CVE-2023-32152	Medium	6.5	29%	-	-
CVE-2023-32148	Medium	6.5	29%	-	-
CVE-2022-20695	Critical	10.0	20%	-	-

Common questions

How do I fix CVE-2025-12421?

Upgrade mattermost server to 11.0.3 or later.

Is CVE-2025-12421 being actively exploited?

Not that we know of. CVE-2025-12421 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.35% is the estimated probability that it will be exploited in the next 30 days. That is higher than 27% of all scored CVEs.

How severe is CVE-2025-12421?

CVE-2025-12421 has a CVSS v3 base score of 9.9, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2025-12421 affect?

Published advisories record a fix for mattermost server (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

Embed a live status badge for CVE-2025-12421

Markdown

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-12-03.