# CVE-2026-9558: Mautic Server-Side Template Injection in theme engine

Source: https://junglewise.ai/threats/cve-2026-9558-mautic-server-side-template-injection-in-theme-engine  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-29. Updated: 2026-07-02  
License: CC BY 4.0 with a link back

CVE-2026-9558 · Severity: critical · CVSS 9.9 · Published 2026-05-29

Mautic, an open-source marketing automation platform, contains a vulnerability in its theme management system. An authorized user with permissions to upload or create themes can exploit this to execute malicious commands on the server. This could lead to a total system takeover, unauthorized access to sensitive customer data, or complete service disruption.

Technologies: [Mautic](https://junglewise.ai/threats/technologies/mautic), [mautic/core (Packagist)](https://junglewise.ai/threats/technologies/packagist-mautic-core). Vendors: [Mautic](https://junglewise.ai/threats/vendors/mautic), [Packagist](https://junglewise.ai/threats/vendors/packagist).

## Quick answers

**Is CVE-2026-9558 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-9558 being exploited in the wild.

**How severe is CVE-2026-9558?** Critical severity, with a CVSS score of 9.9, published 29 May 2026.

**Which products and versions are affected?** Mautic <= 1.3.0, 4.x < 4.4.20, 5.x < 5.2.11, 6.x < 6.0.9, 7.x < 7.1.2, >= 1.3.0, < 4.4.13; >= 5.0.0, < 5.2.11; >= 6.0.0, < 6.0.9; >= 7.0.0, < 7.1.2; mautic/core (Packagist) ECOSYSTEM:introduced=1.3.0.

**Is there a fix for CVE-2026-9558?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-9558 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-9558?** Check whether you run Mautic or mautic/core (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A Server-Side Template Injection (SSTI) vulnerability exists in Mautic's theme engine due to improper neutralization of special elements in Twig templates (CWE-1336). The platform renders uploaded templates without a restricted sandbox or function limitations. An authenticated attacker with 'core:themes:create' permissions can upload a crafted Twig template to achieve Remote Code Execution (RCE) or access restricted system files. The vulnerability is reachable over the network and has been patched in versions 7.1.2, 6.0.9, 5.2.11, and 4.4.20 (via ELTS).

## Affected products

- Mautic Mautic >= 1.3.0, < 4.4.13; >= 5.0.0, < 5.2.11; >= 6.0.0, < 6.0.9; >= 7.0.0, < 7.1.2

## Identifiers

- CVE-2026-9558
- GHSA-9fx4-7cmj-47vg

## Timeline

- 2026-05-29: disclosed
- 2026-07-02: advisory

## References

- [https://api.github.com/users/onurcangnc](https://api.github.com/users/onurcangnc)
- [https://github.com/onurcangnc](https://github.com/onurcangnc)
- [https://api.github.com/users/onurcangnc/gists%7B/gist_id%7D](https://api.github.com/users/onurcangnc/gists%7B/gist_id%7D)
- [https://api.github.com/users/onurcangnc/repos](https://api.github.com/users/onurcangnc/repos)
- [https://avatars.githubusercontent.com/u/55115769?v=4](https://avatars.githubusercontent.com/u/55115769?v=4)
- [https://api.github.com/users/onurcangnc/events%7B/privacy%7D](https://api.github.com/users/onurcangnc/events%7B/privacy%7D)

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