6.5

CVE-2026-26233: Denial of Service via HTTP/2 single packet attack on login endpoint

Analyzed
AliasesGHSA-247x-7qw8-fp98GO-2026-4916
Published 25-03-2026Last modified 27-03-2026

Vulnerability summary

CVE-2026-26233 is a medium (CVSS 6.5) Uncontrolled Resource Consumption vulnerability in mattermost. EPSS estimates a 0.31% chance of exploitation in the next 30 days, higher than 23.9% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 4.3, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
6.5/10
010
Medium · v3.1 (NVD)
EPSS score
0.31%
0%100%
Low · -0.21 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 2 · Related 2
OPENSUSE-SU-2026:21483-1SUSE-SU-2026:1205-1

Timeline

  1. 25-03-2026
    PublishedVulnerability first disclosed.
  2. 27-03-2026
    Last modifiedVulnerability information updated.

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

CVSS metrics

3 scores · 3 sources · 1 version

EPSS trend

Probability

0.31%

Chance of exploitation in the next 30 days

Percentile

24%

Versus all other CVEs

30-day change

Decrease -0.21 pp

From 0.52% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.

Mattermost2 products
  • mattermost11.4.0 | ≥ 11.3.0, ≤ 11.3.1 | ≥ 11.2.0, ≤ 11.2.3 | ≥ 10.11.0, ≤ 10.11.11
  • mattermost_server≥ 10.11.0, < 10.11.12 | ≥ 11.2.0, < 11.2.4 | ≥ 11.3.0, < 11.3.2 | ≥ 11.4.0, < 11.4.1
Github.com/mattermost1 product
  • mattermost-server≥ 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 | ≥ 11.4.0-rc1+incompatible, < 11.4.1+incompatible

2 vendors · 3 products

References

4 links