Incoming webhook user attribution via unvalidated webhook owner

MITRE NVD CVE.ORG JSON API Print: PDF PDF

Summary

CVECVE-2026-9708
StatePUBLISHED
AssignerMattermost
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-13 09:16:25 UTC
Updated2026-07-13 20:39:47 UTC
DescriptionMattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate that an assigned incoming webhook user has access to the target team or channel, which allows a requester with webhook management permissions to create posts or direct messages attributed to another user via crafted incoming webhook configuration and payloads.. Mattermost Advisory ID: MMSA-2026-00683

Risk And Classification

Primary CVSS: v3.1 4.9 MEDIUM from [email protected]

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

EPSS: 0.002100000 probability, percentile 0.112270000 (date 2026-07-14)

Problem Types: CWE-639 | CWE-639 CWE-639: Authorization Bypass Through User-Controlled Key

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.9MEDIUMCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
3.1CNACVSS4.9MEDIUMCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N

CVSS v3.1 Breakdown

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

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/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 11.7.0 11.7.2 semver Not specified
CNA Mattermost Mattermost affected 11.6.0 11.6.4 semver Not specified
CNA Mattermost Mattermost affected 10.11.0 10.11.19 semver Not specified
CNA Mattermost Mattermost unaffected 11.8.0 Not specified
CNA Mattermost Mattermost unaffected 11.7.3 Not specified
CNA Mattermost Mattermost unaffected 11.6.5 Not specified
CNA Mattermost Mattermost unaffected 10.11.20 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: arang (en)

Additional Advisory Data

Solutions

CNA: Update Mattermost to versions 11.8.0, 11.7.3, 11.6.5, 10.11.20 or higher.

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