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CVE-2026-3472 Mattermost CVE debrief

CVE-2026-3472 is a low-severity vulnerability in Mattermost Server versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, and 11.5.x <= 11.5.6. The vulnerability occurs because the application fails to properly apply markdown image rendering restrictions to AI bot tool result posts. This allows an authenticated attacker to inject markdown image syntax into tool result content rendered by a victim's client, potentially leading to data exfiltration to an attacker-controlled server. The Common Vulnerability Scoring System (CVSS) score for this vulnerability is 3.5, indicating a low severity. Mattermost has released an advisory (MMSA-2026-00619) addressing this issue.

Vendor
Mattermost
Product
Mattermost Server
CVSS
LOW 3.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-26
Original CVE updated
2026-06-29
Advisory published
2026-06-26
Advisory updated
2026-06-29

Who should care

Administrators and users of Mattermost Server versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, and 11.5.x <= 11.5.6 should be aware of this vulnerability. An attacker with authenticated access to the Mattermost instance could potentially exploit this vulnerability to exfiltrate data. Therefore, it is crucial for organizations using affected versions to apply the necessary patches or mitigations.

Technical summary

The vulnerability arises from the inadequate application of markdown image rendering restrictions in AI bot tool result posts within Mattermost Server. Specifically, versions 10.11.x up to 10.11.18, 11.6.x up to 11.6.3, and 11.5.x up to 11.5.6 are affected. An authenticated attacker can inject malicious markdown image syntax into tool result content. When a victim's client renders this content, the attacker can potentially exfiltrate data to a server under their control. The CVSS vector for this vulnerability is CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N, indicating a low severity score of 3.5.

Defensive priority

Given the low severity and the requirement for authenticated access, defenders should prioritize patching or mitigating this vulnerability based on their organization's risk assessment. Applying the patches provided by Mattermost for the affected versions (up to 10.11.19, 11.5.7, and 11.6.4) will address this issue.

Recommended defensive actions

  • Apply patches for Mattermost Server versions 10.11.x, 11.5.x, and 11.6.x as per the vendor's advisory.
  • Restrict access to AI bot tool result posts for users who do not require such access.
  • Monitor for suspicious activity related to markdown image syntax injection in tool result content.
  • Implement compensating controls such as additional authentication or authorization checks for sensitive data access.
  • Regularly review and update Mattermost Server configurations to ensure they align with the latest security recommendations.

Evidence notes

The CVE-2026-3472 record and associated NVD details were used to compile this debrief. The Mattermost Advisory ID MMSA-2026-00619 provides additional context on the vulnerability and recommended mitigations. The CVSS score and vector were obtained from the NVD entry for this CVE.

Official resources

This article is AI-assisted and based on the supplied source corpus.