CVE-2025-27715: mattermost server Auth Bypass — Fix

Description

Mattermost versions 9.11.x <= 9.11.8 fail to prompt for explicit approval before adding a team admin to a private channel, which team admins to joining private channels via crafted permalink links without explicit consent from them.

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CVSS v3.1 Score

3.3

LOW

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

Weakness Type (CWE)

CWE-863 Incorrect Authorization

Affected Products

Vendor	Product	Versions
mattermost	mattermost_server	9.11.0 — 9.11.9

References

Advisories & Patches

https://mattermost.com/security-updates

Frequently Asked Questions

What is CVE-2025-27715? +

Mattermost versions 9.11.x <= 9.11.8 fail to prompt for explicit approval before adding a team admin to a private channel, which team admins to joining private channels via crafted permalink links without explicit consent from them. It has a CVSS v3.1 base score of 3.3 (LOW).

How severe is CVE-2025-27715? +

CVE-2025-27715 has a CVSS v3.1 score of 3.3 out of 10, rated LOW. This is a low-severity vulnerability with limited impact.

What products are affected by CVE-2025-27715? +

CVE-2025-27715 affects products from mattermost, specifically: mattermost_server. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-27715? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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