CVE-2026-9558 - A Server-Side Template Injection (SSTI) vulnerability exists in Mautic's theme engine

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CRITICAL

A Server-Side Template Injection (SSTI) vulnerability exists in Mautic's theme engine

Published May 29, 2026

9.9

CRITICAL

CVSS 3.1

EPSS 0.79%

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.

Affected products

Remediation

Vendor solution

There are no official workarounds. To mitigate this vulnerability without upgrading, restrict theme upload and creation permissions (core:themes:create) to only highly trusted administrators.

Weaknesses (1)

CWE-1336

References (4)

Link	Providers	Tags
https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-33276		Advisory
https://github.com/advisories/GHSA-9fx4-7cmj-47vg		Advisory
https://github.com/mautic/mautic/security/advisories/GHSA-9fx4-7cmj-47vg
https://nvd.nist.gov/vuln/detail/CVE-2026-9558