CVE-2026-4274 — Vulnetix

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CVE-2026-4274 PUBLISHED CVSS 5.400000095367432 MEDIUM

Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574

EPSS 0.03% · 7.3th percentile

Risk Scores

CVSS v3.1

5.400000095367432

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

EPSS Score

0.03%

7.3th percentile

Affected Products

Vendor	Product	Versions
Mattermost	Mattermost	11.3.0, 11.2.0, 10.11.0
mattermost	mattermost_server	11.4.0, 11.3.0, 11.4.0
github.com	mattermost/mattermost/server/v8	11.3.0-rc1, 11.2.0-rc1, 10.11.0-rc1

Timeline

Mar 17, 2026 CVE Published
Mar 17, 2026 PoC Published
Mar 17, 2026 PoC Published
Mar 26, 2026 CVE Updated
Mar 27, 2026 EPSS Score
Mar 27, 2026 Coalition ESS Score
Mar 27, 2026 Security Advisory
Apr 16, 2026 PoC Published

References

MMSA-2026-00574 vendor-advisory
https://nvd.nist.gov/vuln/detail/CVE-2026-4274 advisory
https://mattermost.com/security-updates/ advisory
https://github.com/mattermost/mattermost package

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