CVE-2026-6334 PUBLISHED

OAuth authorization code client binding not enforced during token redemption in Mattermost

Assigner: Mattermost
Reserved: 15.04.2026 Published: 18.05.2026 Updated: 18.05.2026

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce client identity binding during the OAuth authorization code redemption flow which allows an authenticated OAuth client to redeem authorization codes issued to a different client via a crafted token exchange request.. Mattermost Advisory ID: MMSA-2026-00570

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N
CVSS Score: 3.1

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	Low
Privileges Required	High	Integrity Impact	Low
User Interaction	Required	Availability Impact	None

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.5.0 to 11.5.1 (incl.) affected from 10.11.0 to 10.11.13 (incl.) Version 11.6.0 is unaffected Version 11.5.2 is unaffected Version 10.11.14 is unaffected

Solutions

Update Mattermost to versions 11.6.0, 11.5.2, 10.11.14 or higher.

Credits

Dylan Haussermann finder

References

MMSA-2026-00570

Problem Types

CWE-305 – Authentication Bypass by Primary Weakness CWE