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CVE-2026-28759

🔶 medium
🔍 Scan for this CVE
Summary

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576

CVSS Score
4.3
Medium
EPSS Score
0.0
Exploit Probability
Published Date
2026-05-18
First Seen: 2026-05-19
📊 Relative Risk Intelligence

This CVE is Lower Risk - more severe than 5.4% of all 327,350 vulnerabilities in our database.

#309,612
Below average severity
Severity Percentile
🎯 CISA SSVC Assessment Updated: May 18, 2026
🔍 Exploitation Status
None
No known exploits
⚙️ Automatable
NO
Requires human interaction
💥 Technical Impact
Partial
Limited system impact
🏆 Discovered By
daw10
SSVC data provided by CISA
Last Modified 2026-05-18
Source NVD 🔗
CVSS Vector 3.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
CWE IDs (Weakness Types)
CWE-863

📦 Affected Products 3

Vendor Product Status Affected Versions
mattermost mattermost_server Affected
> 10.11.0 < 10.11.14
mattermost mattermost_server Affected
> 11.4.0 < 11.4.4
mattermost mattermost_server Affected
> 11.5.0 < 11.5.2

🔗 References 1

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

🔗 Related CVEs 6

CVE ID Severity CVSS EPSS Summary Published
CVE-2026-4915 🔶 medium 6.5 0.1 Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil element... 2026-05-25
CVE-2026-3473 🔶 medium 5.9 0.0 Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate file owne... 2026-05-22
CVE-2026-3636 🔶 medium 4.3 0.0 Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to sanitize team memb... 2026-05-22
CVE-2026-4635 🔶 medium 6.5 0.0 Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to archive the channe... 2026-05-22
CVE-2026-4646 🔶 medium 4.3 0.1 Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate user-supp... 2026-05-22
CVE-2026-5308 🔶 medium 4.9 0.1 Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to enforce request bo... 2026-05-22
These CVEs affect the same products