CVE-2026-9558

SSTI in Mautic Theme Engine Allows Authenticated Remote Code Execution

Published May 29, 2026 CVSS 3.1 · 9.9 Critical EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Workaround

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.

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-9fx4-7cmj-47vg Mautic has Server-Side Template Injection (SSTI) in Theme Templates
History
Type Values Removed Values Added
Title SSTI in Mautic Theme Engine Allows Authenticated Remote Code Execution
First Time appeared Mautic
Mautic mautic
Vendors & Products Mautic
Mautic mautic
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Weaknesses CWE-1336
References
Metrics cvssV3_1

{'score': 9.9, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Mautic
Published
Updated
May 29, 2026, 10:49 AM
Reserved
May 26, 2026, 8:36 AM
Status
Deferred
Published
May 29, 2026, 11:16 AM
Modified
Jul 21, 2026, 12:10 PM