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CVE-2026-6342

Group prefix matching bypass for subscriptions

MEDIUM
4.3
CVSS Score
Published: May 18, 2026 at 07:00 AM UTC
Updated: October 14, 2026 at 08:10 PM UTC
2 products affected across 1 vendorMattermost ServerMattermost

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Severity
MEDIUM4.3
Exploit prediction
EPSS 0.2%
SSVC
No known exploit

Description

Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to appropriately check for valid namespaces which allows plugin users to create subscriptions to groups that were not whitelisted via creating groups that share the same prefix as a whitelisted group. Mattermost Advisory ID: MMSA-2026-00601

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mattermost Server· Mattermost
95%
10.13.0 ≤ v ≤ 10.13.1111.1.0 ≤ v ≤ 11.1.511.3.0 ≤ v ≤ 11.3.4
Mattermost· Mattermost
90%
0 ≤ v ≤ 10.13.110 ≤ v ≤ 11.1.50 ≤ v ≤ 11.3.4
Vendor states this is fixed in 10.11.14 (unaffected)
Vendor states this is fixed in 11.4.4 (unaffected)
Vendor states this is fixed in 11.5.2 (unaffected)
Vendor states this is fixed in 11.6.0 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (1)

Vendor Advisory
Source: cverecord
https://mattermost.com/security-updates

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

4.3MEDIUMMattermost
Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-863

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