CVE-2026-20719: DoS via URL Previews Rendering Malicious SVGs

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-25 · updated 2026-06-17
Weakness: CWE-754

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 prevent rendering of external SVGs on link embeds which allows unauthenticated users to crash the Mattermost webapp and desktop app via creating an issue or PR on GitHub.. Mattermost Advisory ID: MMSA-2026-00595

Affected products

Mattermost: from 10.11.0 before 10.11.12; from 11.2.0 before 11.2.4; from 11.3.0 before 11.3.2; from 11.4.0 before 11.4.1 — fixed in 10.11.12, 11.2.4, 11.3.2, 11.4.1

How to fix

Upgrade to a fixed version: Mattermost 10.11.12, 11.2.4, 11.3.2, 11.4.1. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

Get alerted when CVE-2026-20719 or the next vulnerability affects your stack