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

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Summary

CVECVE-2026-6334
StatePUBLISHED
AssignerMattermost
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-18 08:16:14 UTC
Updated2026-05-29 19:11:30 UTC
DescriptionMattermost 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

Risk And Classification

Primary CVSS: v3.1 3.8 LOW from [email protected]

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

EPSS: 0.000250000 probability, percentile 0.074150000 (date 2026-05-26)

Problem Types: CWE-305 | CWE-305 CWE-305 – Authentication Bypass by Primary Weakness

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary3.8LOWCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:N
3.1[email protected]Secondary3.1LOWCVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N
3.1CNACVSS3.1LOWCVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

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

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Mattermost Mattermost Server All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mattermost Mattermost affected 11.5.0 11.5.1 semver Not specified
CNA Mattermost Mattermost affected 10.11.0 10.11.13 semver Not specified
CNA Mattermost Mattermost unaffected 11.6.0 Not specified
CNA Mattermost Mattermost unaffected 11.5.2 Not specified
CNA Mattermost Mattermost unaffected 10.11.14 Not specified

References

ReferenceSourceLinkTags
mattermost.com/security-updates [email protected] mattermost.com Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Dylan Haussermann (en)

Additional Advisory Data

Solutions

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

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