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CVE-2025-11777

Cross-team channel membership access

MEDIUM
4.3
CVSS Score
Published: November 13, 2025 at 05:32 PM UTC
Updated: October 19, 2026 at 01:10 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 versions 10.11.x <= 10.11.3, 10.5.x <= 10.5.11 fail to properly validate team membership permissions in the Add Channel Member API which allows users from one team to access user metadata and channel membership information from other teams via the API endpoint

Affected

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

Mattermost Server· Mattermost
95%
10.11.0 ≤ v < 10.11.410.5.0 ≤ v < 10.5.12
Mattermost· Mattermost
90%
10.11.0 ≤ v ≤ 10.11.310.5.0 ≤ v ≤ 10.5.1110.11.010.5.0
Vendor states this is fixed in 10.11.4 (unaffected)
Vendor states this is fixed in 10.5.12 (unaffected)
Vendor states this is fixed in 11.0.0 (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

4.3MEDIUM[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
LOW
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-863

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