Is CVE-2026-26233 in the CISA KEV catalog?

No. CVE-2026-26233 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-26233?

CVE-2026-26233 has a CVSS v3 base score of 4.3 (MEDIUM).

What is the EPSS score for CVE-2026-26233?

CVE-2026-26233 has an EPSS score of 0.30% (22th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-26233?

Upgrade mattermost server to 11.4.1 or later.

CVE & CISA-KEV Catalog

CVE-2026-26233

MEDIUM

4.3

CVSS v3

NVD

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

CWE-400Resource Exhaustion

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 11.4.0, < 11.4.1Fixed in:11.4.1CVE-2026-26233derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

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

Exploit Intelligence

0.30%probability of exploitation in 30 days

22ndpercentile

Low risk: more likely to be exploited than 22% of all known CVEs.

References

Vendor Advisory1

mattermost.com

Related Vulnerabilities

Other CWE-400 (Resource Exhaustion) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-44487	High	7.5	100%	KEV	Fix
CVE-2021-44228	Critical	10.0	100%	KEV + Ransom	Fix
CVE-2011-3192	High	7.8	99%	-	Fix
CVE-2019-11478	Medium	5.3	95%	-	Fix
CVE-2024-25617	Medium	5.3	89%	-	Fix
CVE-2018-1000115	High	7.5	89%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-03-26.