CVE-2026-9558
Mautic has Server-Side Template Injection (SSTI) in Theme Templates
Description
### Summary 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. ### Impact An authenticated user with theme upload and creation privileges can bypass boundaries to execute arbitrary system commands on the hosting server (Remote Code Execution) or access restricted system files and configuration settings. ### Patched Versions This security issue has been addressed in the following releases: * **7.1.2** * **6.0.9** * **5.2.11** For users on Mautic 4.x, this fix is available in: * **4.4.20** via [ELTS](https://mautic.org/extended-long-term-support-elts/) Mautic strongly recommend upgrading to a patched version immediately. ### Workarounds 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.
How to fix CVE-2026-9558
No fixed version has been published yet. Mitigate by removing the affected package or applying upstream guidance from the references below.
- —no fix listed
Is CVE-2026-9558 being exploited?
Low — EPSS is 0.4%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- >= 1.3.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | CRITICAL9.9 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H |