---
title: "CVE-2026-9558: Mautic has Server-Side Template Injection (SSTI) in Theme Templates"
url: https://erroneo.us/security/cve/CVE-2026-9558/
description: "CVE-2026-9558 (mautic/core (Composer (PHP))): A Server-Side Template Injection (SSTI) vulnerability exists in Mautic's theme engine. The platform renders…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-29
date_modified: 2026-07-02
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-9558"
kev: false
cvss: 9.9
epss: 0.00789
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-9558: Mautic has Server-Side Template Injection (SSTI) in Theme Templates

**Signal:** Critical, preconditions apply. Severe if exploited, but exploitation needs conditions that may not apply to you. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.8% , percentile 56: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 56% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Needs an account (low (any account)). Exposure depends on who can log in.
- Only applies if your dependency tree includes mautic/core (Composer (PHP)) >= 1.3.0, < 4.4.13, no fixed version listed ; mautic/core (Composer (PHP)) >= 5.0.0, < 5.2.11, fixed in 5.2.11 ; mautic/core (Composer (PHP)) >= 6.0.0, < 6.0.9, fixed in 6.0.9 ; mautic/core (Composer (PHP)) >= 7.0.0, < 7.1.2, fixed in 7.1.2 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- Composer (PHP) `mautic/core` >= 1.3.0, < 4.4.13 → fixed: none listed
- Composer (PHP) `mautic/core` >= 5.0.0, < 5.2.11 → fixed: 5.2.11
- Composer (PHP) `mautic/core` >= 6.0.0, < 6.0.9 → fixed: 6.0.9
- Composer (PHP) `mautic/core` >= 7.0.0, < 7.1.2 → fixed: 7.1.2

## Affected products (CVE record)

-  mautic/core: 1.3.0 < 4.4.20, 5.0.0 < 5.2.11, 6.0.0 < 6.0.9, 7.0.0 < 7.1.2

## Severity

- Mautic CVSS 3.1: 9.9 `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.9 `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.79% probability of exploitation activity in the next 30 days; percentile 56.

## Sources

- [GitHub Advisory GHSA-9fx4-7cmj-47vg](https://github.com/advisories/GHSA-9fx4-7cmj-47vg)
- [CVE.org record CVE-2026-9558](https://www.cve.org/CVERecord?id=CVE-2026-9558)
- [NVD entry CVE-2026-9558](https://nvd.nist.gov/vuln/detail/CVE-2026-9558)
- [github.com](https://github.com/mautic/mautic/security/advisories/GHSA-9fx4-7cmj-47vg)

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Source page: https://erroneo.us/security/cve/CVE-2026-9558/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt