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Mattermost doesn't enforce client identity binding during the OAuth authorization code redemption flow

Low severity GitHub Reviewed Published May 18, 2026 to the GitHub Advisory Database • Updated Jun 1, 2026

Package

gomod github.com/mattermost/mattermost-server (Go)

Affected versions

< 5.3.2-0.20260318173148-e9ae890a013b

Patched versions

5.3.2-0.20260318173148-e9ae890a013b
gomod github.com/mattermost/mattermost/server/v8 (Go)
>= 11.5.0, < 11.5.2
>= 10.11.0, < 10.11.14
< 8.0.0-20260318173148-e9ae890a013b
11.5.2
10.11.14
8.0.0-20260318173148-e9ae890a013b

Description

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

References

Published by the National Vulnerability Database May 18, 2026
Published to the GitHub Advisory Database May 18, 2026
Reviewed Jun 1, 2026
Last updated Jun 1, 2026

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
High
User interaction
Required
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(2nd percentile)

Weaknesses

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. Learn more on MITRE.

CVE ID

CVE-2026-6334

GHSA ID

GHSA-jp3f-x449-4q75

Source code

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