Skip to content

Mattermost doesn't rate limit login requests, allowing DoS

Moderate severity GitHub Reviewed Published Mar 25, 2026 to the GitHub Advisory Database • Updated Apr 6, 2026

Package

gomod github.com/mattermost/mattermost-server (Go)

Affected versions

>= 11.4.0-rc1, < 11.4.1
>= 11.3.0-rc1, < 11.3.2
>= 11.2.0-rc1, < 11.2.4
>= 10.11.0-rc1, < 10.11.12

Patched versions

11.4.1
11.3.2
11.2.4
10.11.12

Description

Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to rate limit login requests which allows unauthenticated remote attackers to cause denial of service (server crash and restart) via HTTP/2 single packet attack with 100+ parallel login requests.. Mattermost Advisory ID: MMSA-2025-00566

References

Published by the National Vulnerability Database Mar 25, 2026
Published to the GitHub Advisory Database Mar 25, 2026
Reviewed Mar 31, 2026
Last updated Apr 6, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(26th percentile)

Weaknesses

Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource. Learn more on MITRE.

CVE ID

CVE-2026-26233

GHSA ID

GHSA-247x-7qw8-fp98

Source code

Loading Checking history
See something to contribute? Suggest improvements for this vulnerability.