Is CVE-2026-4054 in the CISA KEV catalog?

No. CVE-2026-4054 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-4054?

CVE-2026-4054 has a CVSS v3 base score of 4.3 (MEDIUM).

What is the EPSS score for CVE-2026-4054?

CVE-2026-4054 has an EPSS score of 0.24% (15th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-4054?

Upgrade mattermost server to 11.5.2 or later.

CVE & CISA-KEV Catalog

CVE-2026-4054

MEDIUM

4.3

CVSS v3

NVD

Description

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 Fail to validate the response body of proxied images, which allows a remote attacker to enact client-side DoS via an SVG file served from an attacker-controlled origin under a non-SVG Content-Type header (e.g. image/png) embedded in an og:image meta tag or Markdown image link.. Mattermost Advisory ID: MMSA-2026-00630

CWE-754

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 11.5.0, < 11.5.2Fixed in:11.5.2CVE-2026-4054derived 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 RequiredNone

User InteractionRequired

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

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

Exploit Intelligence

0.24%probability of exploitation in 30 days

15thpercentile

Low risk: more likely to be exploited than 15% of all known CVEs.

References

Vendor Advisory1

mattermost.com

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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 2026-05-18.