Is CVE-2026-2456 in the CISA KEV catalog?

No. CVE-2026-2456 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-2456?

CVE-2026-2456 has a CVSS v3 base score of 5.3 (MEDIUM).

What is the EPSS score for CVE-2026-2456?

CVE-2026-2456 has an EPSS score of 0.17% (6th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-2456?

Upgrade mattermost server to 11.3.1 or later.

CVE & CISA-KEV Catalog

CVE-2026-2456

MEDIUM

5.3

CVSS v3

NVD

Description

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 Mattermost fails to limit the size of responses from integration action endpoints, which allows an authenticated attacker to cause server memory exhaustion and denial of service via a malicious integration server that returns an arbitrarily large response when a user clicks an interactive message button.. Mattermost Advisory ID: MMSA-2026-00571

CWE-789

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 11.3.0, < 11.3.1Fixed in:11.3.1CVE-2026-2456derived 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 ComplexityHigh

Privileges RequiredNone

User InteractionRequired

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Exploit Intelligence

0.17%probability of exploitation in 30 days

6thpercentile

Low risk: more likely to be exploited than 6% of all known CVEs.

References

Vendor Advisory1

mattermost.com

Related Vulnerabilities

Other CWE-789 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2022-30522	High	7.5	90%	-	Fix
CVE-2026-49975	High	7.5	11%	-	Fix
CVE-2025-27533	High	7.5	8.6%	-	Fix
CVE-2017-7651	High	7.5	5.3%	-	Fix
CVE-2021-31811	Medium	5.5	3.4%	-	-
CVE-2021-27906	Medium	5.5	3.3%	-	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 2026-03-18.