Plugin bot username conflict allows user account to be used as bot identity in Mattermost Server

MITRE NVD CVE.ORG JSON API Print: PDF PDF

Summary

CVECVE-2026-6046
StatePUBLISHED
AssignerMattermost
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-12 17:16:26 UTC
Updated2026-06-18 14:33:35 UTC
DescriptionMattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

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

EPSS: 0.001900000 probability, percentile 0.086720000 (date 2026-06-22)

Problem Types: CWE-200 | CWE-200 CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
3.1CNACVSS5.3MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

CVSS v3.1 Breakdown

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

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/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 11.6.0 11.6.1 semver Not specified
CNA Mattermost Mattermost affected 11.5.0 11.5.4 semver Not specified
CNA Mattermost Mattermost affected 10.11.0 10.11.15 semver Not specified
CNA Mattermost Mattermost affected 10.11.0 10.11.16 semver Not specified
CNA Mattermost Mattermost unaffected 11.7.0 Not specified
CNA Mattermost Mattermost unaffected 11.6.2 Not specified
CNA Mattermost Mattermost unaffected 11.5.5 Not specified
CNA Mattermost Mattermost unaffected 10.11.16 Not specified
CNA Mattermost Mattermost unaffected 10.11.17 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: insomnia1102 (en)

Additional Advisory Data

Solutions

CNA: Update Mattermost to versions 11.7.0, 11.6.2, 11.5.5, 10.11.16, 10.11.17 or higher.

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