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Mautic has Server-Side Template Injection (SSTI) in Theme Templates

Critical severity GitHub Reviewed Published May 29, 2026 in mautic/mautic

Package

composer mautic/core (Composer)

Affected versions

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

Patched versions

5.2.11
6.0.9
7.1.2

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:

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.

References

@patrykgruszka patrykgruszka published to mautic/mautic May 29, 2026
Published by the National Vulnerability Database May 29, 2026
Published to the GitHub Advisory Database Jul 2, 2026
Reviewed Jul 2, 2026

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(44th percentile)

Weaknesses

Improper Neutralization of Special Elements Used in a Template Engine

The product uses a template engine to insert or process externally-influenced input, but it does not neutralize or incorrectly neutralizes special elements or syntax that can be interpreted as template expressions or other code directives when processed by the engine. Learn more on MITRE.

CVE ID

CVE-2026-9558

GHSA ID

GHSA-9fx4-7cmj-47vg

Source code

Credits

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