Mattermost: Incorrect Implementation of Authentication Algorithm
CVE-2025-12421 is a critical-severity incorrect implementation of authentication algorithm vulnerability in Mattermost, with a CVSS 3.1 base score of 9.9 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected Mattermost versions: 11.0.0 through 11.0.2; 10.12.0 through 10.12.1; 10.11.0 through 10.11.4, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.45% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Mattermost Server to 10.5.13 or 10.11.5 or 10.12.2 or 11.0.3, whichever matches your release line, or a later version.
- Read the advisory on mattermost.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Mattermost | Mattermost | 11.0.0 through 11.0.2; 10.12.0 through 10.12.1; 10.11.0 through 10.11.4; 10.5.0 through 10.5.12 | Not stated |
| Mattermost | Mattermost Server | 10.5.0 up to, but not including, 10.5.13; 10.11.0 up to, but not including, 10.11.5; 10.12.0 up to, but not including, 10.12.2; 11.0.0 up to, but not including, 11.0.3 | 10.5.13, 10.11.5, 10.12.2, 11.0.3 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H. Scored by CNA (mattermost.com).
Official 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).
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Incorrect Implementation of Authentication Algorithm
The requirements for the product dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect.
More Incorrect Implementation of Authentication Algorithm vulnerabilities (CWE-303)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other vulnerabilities in Mattermost
- 8.0 High severity
- 7.1 High severity
- 9.3 Critical severity
- 7.1 High severity
Recent Incorrect Implementation of Authentication Algorithm vulnerabilities
- 9.9 Critical severity
- 7.5 High severity
- 8.1 High severity
- 7.3 High severity
- 7.5 High severity
- 9.8 Critical severity
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