9.9

CVE-2025-12421: Account Takeover via Code Exchange Endpoint

Analyzed
AliasesGHSA-mp6x-97xj-9x62GO-2025-4170
Published 27-11-2025Last modified 26-02-2026

Vulnerability summary

CVE-2025-12421 is a critical (CVSS 9.9) vulnerability in mattermost. EPSS estimates a 0.45% chance of exploitation in the next 30 days, higher than 38.8% of scored vulnerabilities.

Priority
Prioritisesevere

Severe, CVSS 9.9 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 0% (FIRST, 03-11-2026)

Source freshness unavailable

How is this decided?
CVSS score
9.9/10
010
Critical · v3.1 (CVE.org)
EPSS score
0.45%
0%100%
Low · +0.10 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 2 · Related 2
OPENSUSE-SU-2026:21483-1SUSE-SU-2026:0037-1

Timeline

  1. 27-11-2025
    PublishedVulnerability first disclosed.
  2. 26-02-2026
    Last modifiedVulnerability information updated.

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 metrics

3 scores · 3 sources · 1 version

EPSS trend

Probability

0.45%

Chance of exploitation in the next 30 days

Percentile

39%

Versus all other CVEs

30-day change

Increase +0.10 pp

From 0.34% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.

Github.com/mattermost/mattermost-server2 products
  • v5All versions (No fix recorded)
  • v6All versions (No fix recorded)
Mattermost2 products
  • mattermost≥ 11.0.0, ≤ 11.0.2 | ≥ 10.12.0, ≤ 10.12.1 | ≥ 10.11.0, ≤ 10.11.4 | ≥ 10.5.0, ≤ 10.5.12
  • mattermost_server≥ 10.5.0, < 10.5.13 | ≥ 10.11.0, < 10.11.5 | ≥ 10.12.0, < 10.12.2 | ≥ 11.0.0, < 11.0.3
Github.com/mattermost1 product
  • mattermost-server≥ 11.0.0, < 11.0.3 | ≥ 10.12.0, < 10.12.2 | ≥ 10.11.0, < 10.11.5 | ≥ 10.5.0, < 10.5.13 | All versions (No fix recorded)
Github.com/mattermost/mattermost/server1 product
  • v8< 8.0.0-20251022210333-acda1fb5dd46

4 vendors · 6 products

References

8 links