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CVE-2026-9558 — Vulnerability in mautic/core — CVE Details

CRITICAL

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

Published July 2, 2026Updated September 10, 2026Source: osv

Summary

### 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: * **4.4.20** via [ELTS](https://mautic.org/extended-long-term-support-elts/) 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.

Advisory Timeline

  • First published July 2, 2026 (102 days ago).
  • Last revised September 10, 2026 — 69 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

Composer
Update mautic/core to 5.2.11 or later
composer require "mautic/core:^5.2.11"
Composer
Update mautic/core to 7.1.2 or later
composer require "mautic/core:^7.1.2"
Composer
Update mautic/core to 6.0.9 or later
composer require "mautic/core:^6.0.9"

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (4)

Affects 1 ecosystem: packagist (1).

PackageEcosystemAffectedFixed In
mautic/core
packagist
1.3.0, 1.3.1, 1.4.0, 1.4.1 (+176 more)Range-based data available
mautic/core
packagist
5.0.0, 5.0.1, 5.0.2, 5.0.3 (+14 more)5.2.11
mautic/core
packagist
7.0.0, 7.0.1, 7.0.2, 7.1.0 (+2 more)7.1.2
mautic/core
packagist
6.0.0, 6.0.1, 6.0.2, 6.0.3 (+5 more)6.0.9

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 9.9 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

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

References

Frequently Asked Questions

What is CVE-2026-9558?
Mautic has Server-Side Template Injection (SSTI) in Theme Templates This vulnerability has been assigned a severity rating of CRITICAL (CVSS score: 9.9/10).
How do I check if my project is affected by CVE-2026-9558?
CVE-2026-9558 affects mautic/core. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2026-9558 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
9.9

Exploitation is straightforward and causes maximum impact. Patch immediately.

Also Known As

GHSA-9fx4-7cmj-47vg

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