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MEDIUM · 6.5

CVE-2026-5163

Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private cha...

Vulnerability Description

Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645

CVSS Score

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
NONE
Availability
NONE

Affected Products

VendorProductVersions
MattermostMattermost Server>= 11.5.0, < 11.5.2

Related Weaknesses (CWE)

CWE-862

References

FAQ

What is CVE-2026-5163?

CVE-2026-5163 is a vulnerability with a CVSS score of 6.5 (MEDIUM). Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private cha...

How severe is CVE-2026-5163?

CVE-2026-5163 has been rated MEDIUM with a CVSS base score of 6.5/10. Review the CVSS metrics above for detailed severity breakdown.

Is there a patch for CVE-2026-5163?

Check the references section above for vendor advisories and patch information. Affected products include: Mattermost Mattermost Server.