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Review reviewHigh

CVE-2026-5308

Mattermost Mattermost, mattermost server

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 body size limits on plugin HTTP endpoints which allows an attacker to cause a denial of service via crafted oversized HTTP requests.. Mattermost Advisory ID: MMSA-2026-00646

CVSS
7.5
EPSS
0.25%
17.0% percentile
CISA KEV
Not listed
Published
2026.05.22
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.25%
Technical severityCVSS 7.5

Vulnerability overview

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 body size limits on plugin HTTP endpoints which allows an attacker to cause a denial of service via crafted oversized HTTP requests.. Mattermost Advisory ID: MMSA-2026-00646

Affected product and versions

Product
Mattermost Mattermost, mattermost server
Affected versions
>= 11.6.0 <= 11.6.0, >= 11.5.0 <= 11.5.3, >= 11.4.0 <= 11.4.4, >= 10.11.0 <= 10.11.14, >= 10.11.0 < 10.11.15, >= 11.4.0 < 11.4.5, >= 11.5.0 < 11.5.4, >= 11.6.0 < 11.6.1
Fixed versions
10.11.15, 11.4.5, 11.5.4, 11.6.1

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that Mattermost Mattermost, mattermost server and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE
CWE-400