Mattermost Desktop App fails to restrict the allow list of domains which NTLM credentials are passed

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Summary

CVECVE-2026-6517
StatePUBLISHED
AssignerMattermost
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-15 14:16:37 UTC
Updated2026-06-16 16:54:47 UTC
DescriptionMattermost Desktop App versions <=6.1 5.5.13.0 fail to restrict the allow list of domains to which NTLM credentials were forwarded to in the Mattermost Desktop App which allows any user on a server without the image proxy enabled to intercept other users credentials via embedding an image that routes to an external web server. Mattermost Advisory ID: MMSA-2026-00651

Risk And Classification

Primary CVSS: v3.1 7.7 HIGH from [email protected]

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

EPSS: 0.001870000 probability, percentile 0.083320000 (date 2026-06-23)

Problem Types: CWE-522 | CWE-522 CWE-522: Insufficiently Protected Credentials

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary7.7HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
3.1[email protected]Secondary6.3MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N
3.1CNACVSS6.3MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N

CVSS v3.1 Breakdown

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

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Mattermost Mattermost Desktop All - All All
Application Mattermost Mattermost Desktop All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mattermost Mattermost affected 5.5.13 semver Not specified
CNA Mattermost Mattermost unaffected 6.2.0 Not specified
CNA Mattermost Mattermost unaffected 5.13.6.0 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: falke (en)

Additional Advisory Data

Solutions

CNA: Update Mattermost Desktop App to versions 6.2.0, 5.13.6.0 or higher.

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