Raw vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:HSummary
CVE-2025-12421 is a critical-severity Incorrect Implementation of Authentication Algorithm (CWE-303) vulnerability in Mattermost Mattermost Server. Its CVSS base score is 9.9 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique External Remote Services (T1133); ranked at the 27th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2025-12421 is a critical authentication vulnerability in Mattermost, affecting versions 11.0.x up to and including 11.0.2, 10.12.x up to 10.12.1, 10.11.x up to 10.11.4, and 10.5.x up to 10.5.12. The issue arises from a failure to verify that the token used during the code exchange originates from the same authentication flow. This is classified under CWE-303 (Incorrect Check of Function Return Value) and carries a CVSS v3.1 base score of 9.9 (AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H). Exploitation requires the ExperimentalEnableAuthenticationTransfer feature to be enabled (default: enabled) and RequireEmailVerification to be disabled (default: disabled).
An authenticated user with low privileges can exploit this vulnerability remotely over the network with low attack complexity and no user interaction. The attacker crafts a specially formatted email address while switching authentication methods, then sends a request to the /users/login/sso/code-exchange endpoint. This allows takeover of another user's account by hijacking the authentication flow, potentially granting full access to the victim's data and privileges due to the changed scope and high impacts on confidentiality, integrity, and availability.
Mattermost has published details on mitigations in their security updates, available at https://mattermost.com/security-updates. Security practitioners should review this advisory for patch information and configuration guidance to address the vulnerability.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-199833
Vulnerability Data
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…
more
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(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation at post-design stages directly uncovers incorrect implementations of required authentication algorithms.
Requiring documented development processes, standards, and tools reduces the chance that an established authentication algorithm is coded incorrectly.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly require correct implementation of authentication algorithms.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Secure authentication control directly requires correct implementation of authentication algorithms.
Security testing can detect flawed authentication implementations but does not prevent them by itself.
Cryptography control addresses proper use of authentication algorithms but is broader than authentication alone.
Secure development lifecycle includes verification steps that can catch incorrect authentication implementations.
Application security requirements can specify correct authentication algorithm use but do not guarantee correct implementation.
Secure coding practices reduce the likelihood of incorrect authentication algorithm implementation.