CVE-2026-3472: Markdown image rendering bypass in AI bot tool result posts in Mattermost

Severity: low (CVSS 3.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-26 · updated 2026-06-29
Weakness: CWE-693

Description

Mattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to properly apply markdown image rendering restrictions to AI bot tool result posts, which allows an authenticated attacker to exfiltrate data to an attacker-controlled server via injecting markdown image syntax into tool result content rendered by a victim's client.. Mattermost Advisory ID: MMSA-2026-00619

Affected products

Mattermost: from 10.11.0 before 10.11.19; from 11.5.0 before 11.5.7; from 11.6.0 before 11.6.4 — fixed in 10.11.19, 11.5.7, 11.6.4

How to fix

Upgrade to a fixed version: Mattermost 10.11.19, 11.5.7, 11.6.4. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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