Medium severity · published May 15, 2026
CVE-2026-4054
SVG content served through Mattermost image proxy despite Content-Type restrictions causes client-side denial of service
6.5
CVSS
0.2%
EPSS
No
On KEV
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
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 15% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.5.0 through 11.5.1; 10.11.0 through 10.11.13; 11.4.0 through 11.4.3 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.14; 11.4.0 before 11.4.4; 11.5.0 before 11.5.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-4054
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-4054
Vendor Advisory
https://mattermost.com/security-updates
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