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🛡️ CVE-2026-6334 — mattermost-server

🟢 CVSS 3.1 — Low ✅ No Known Exploit CWE-305 NVD
3.1
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Mattermost doesn't enforce client identity binding during the OAuth authorization code redemption flow in github.com/mattermost/mattermost-server

Mattermost doesn't enforce client identity binding during the OAuth authorization code redemption flow in github.com/mattermost/mattermost-server.

NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions.

(If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.)

The additional affected modules and versions are: github.com/mattermost/mattermost-server/v5 before v5.3.2-0.20260318173148-e9ae890a013b.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs administrative privileges on the target. A user must be tricked into taking some action. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality low, integrity low, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: High — the attacker first has to win a race, learn a secret or otherwise prepare the target.
  • Privileges required: High — administrative rights are needed first.
  • User interaction: Required — someone has to click, open or visit something.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: Low — limited, and the attacker does not choose what is affected.
  • Integrity impact: Low — limited, and the attacker does not choose what is affected.
  • Availability impact: None.

Weakness class

CVE-2026-6334 is classified as CWE-305: Authentication Bypass by Primary Weakness. The authentication algorithm is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.

Affected software

CVE-2026-6334 is recorded against 5 packages.

  • github.com/mattermost/mattermost-server
  • github.com/mattermost/mattermost-server/v5
  • github.com/mattermost/mattermost-server/v6
  • github.com/mattermost/mattermost/server/v8
  • mattermost-server (from 11.5.0 up to 11.5.2)

Timeline and source

Published on 25 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Advisory)
nvd.nist.gov (Advisory)
github.com (Web)
mattermost.com (Web)

Other advisories for this package

github.com/mattermost/mattermost-server has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-305: Authentication Bypass by Primary Weakness) in other software:

Details

Severity LOW
CVSS Score 3.1
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N
CWE CWE-305
Public Exploit ✅ No
Source NVD
Published 2026-06-25
Updated 2026-08-20
Modified 2026-06-25
Fix URL N/A

Affected Packages

Software From version Fixed in
github.com/mattermost/mattermost-server — —
github.com/mattermost/mattermost-server/v5 — —
github.com/mattermost/mattermost-server/v6 — —
github.com/mattermost/mattermost/server/v8 — —
mattermost-server 11.5.0 11.5.2

Similar Threats

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