CVE-2026-9558 Mautic has Server-Side Template Injection (SSTI) in Theme Templates
Authenticated users can execute arbitrary code or read system files via Server-Side Template Injection in Mautic's theme engine.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-9558?
CVE-2026-9558 is a critical code injection vulnerability in mautic/core, published on 29 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Weakness: CWE-1336
Which versions are affected by CVE-2026-9558?
8 open source packages ship an affected version, including mautic/core.
| Package | Affected | Fixed in |
|---|---|---|
mautic/core Packagist | From 1.3.0 | None |
mautic/core Packagist | From 1.3.0 | None |
mautic/core Packagist | From 5.0.0 | 5.2.11 |
mautic/core Packagist | From 5.0.0 | 5.2.11 |
mautic/core Packagist | From 6.0.0 | 6.0.9 |
mautic/core Packagist | From 6.0.0 | 6.0.9 |
2 more packages
mautic/core Packagist | From 7.0.0 | 7.1.2 |
mautic/core Packagist | From 7.0.0 | 7.1.2 |
How do I fix CVE-2026-9558?
Upgrade mautic/core to a fixed version for your release line: 5.2.11, 6.0.9 or 7.1.2.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-9558 being exploited?
There is no known exploitation of CVE-2026-9558 in the wild and no public exploit code.
Public exploit code: 2 proofs of concept on GitHub.
Sources
Also known as GHSA-9fx4-7cmj-47vg.