CVE-2026-9558 — core
CRITICALCVE-2026-9558 is a critical-severity (CVSS 9.9) CWE-1336 vulnerability in mautic/core. A fix is available for mautic/core — see the affected versions and patch details below.
Mautic has Server-Side Template Injection (SSTI) in Theme Templates
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-9558.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-9558 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
mautic/core🐘mautic/core🐘mautic/core🐘mautic/coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
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
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | mautic/core | ≥ 1.3.0 | No fix |
| 🐘Packagist | mautic/core | ≥ 5.0.0&&< 5.2.11 | 5.2.11composer require mautic/core:^5.2.11 |
| 🐘Packagist | mautic/core | ≥ 6.0.0&&< 6.0.9 | 6.0.9composer require mautic/core:^6.0.9 |
| 🐘Packagist | mautic/core | ≥ 7.0.0&&< 7.1.2 | 7.1.2composer require mautic/core:^7.1.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mautic/core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
No patched version of mautic/core has shipped for CVE-2026-9558 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-9558 in your dependencies?
Find it across Packagist, including transitive dependencies.