CVE-2026-9558 — CRITICAL (9.9)

Vulnerability Description

A Server-Side Template Injection (SSTI) vulnerability exists in Mautic's theme engine. The platform renders uploaded Twig templates without a sandbox or strict function restrictions. Authenticated users with permissions to create or upload themes can abuse this to execute arbitrary code on the hosting server (Remote Code Execution) or access restricted system files and configuration settings.

CVSS Score

9.9

CRITICAL

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

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

CHANGED

Confidentiality

HIGH

Integrity

HIGH

Availability

HIGH

Related Weaknesses (CWE)

CWE-1336

References

https://github.com/mautic/mautic/security/advisories/GHSA-9fx4-7cmj-47vg

FAQ

What is CVE-2026-9558?

CVE-2026-9558 is a vulnerability with a CVSS score of 9.9 (CRITICAL). A Server-Side Template Injection (SSTI) vulnerability exists in Mautic's theme engine. The platform renders uploaded Twig templates without a sandbox or strict function restrictions. Authenticated use...

How severe is CVE-2026-9558?

CVE-2026-9558 has been rated CRITICAL with a CVSS base score of 9.9/10. This is considered a critical vulnerability requiring immediate attention.

Is there a patch for CVE-2026-9558?

Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.