CVE-2026-9558
CRITICALCVE-2026-9558 is a critical-severity (CVSS 9.9) CWE-1336 vulnerability in mautic/core. O3 Security confirms whether CVE-2026-9558 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-9558 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 369,023 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | mautic/core | ≥ 1.3.0 | No fix |
| 🐘Packagist | mautic/core | ≥ 5.0.0&&< 5.2.11 | 5.2.11 |
| 🐘Packagist | mautic/core | ≥ 6.0.0&&< 6.0.9 | 6.0.9 |
| 🐘Packagist | mautic/core | ≥ 7.0.0&&< 7.1.2 | 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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.
How O3 protects you
O3 pinpoints whether CVE-2026-9558 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-9558. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-9558 in your dependencies?
O3 detects CVE-2026-9558 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.