CVE-2026-9558 (CVSS 9.9)

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.

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CVSS v3.1 Score

9.9

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0044

Probability of exploitation

0.35%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-1336 CWE-1336

References

Other References

https://github.com/mautic/mautic/security/advisories/GHSA-9fx4-7cmj-47vg

Frequently Asked Questions

What is CVE-2026-9558? +

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. It has a CVSS v3.1 base score of 9.9 (CRITICAL).

How severe is CVE-2026-9558? +

CVE-2026-9558 has a CVSS v3.1 score of 9.9 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0044, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-9558? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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