Security Digest · Vulnerability record
CVE-2026-9558: Mautic has Server-Side Template Injection (SSTI) in Theme Templates
A Server-Side Template Injection (SSTI) vulnerability exists in Mautic's theme engine.
CVSS 9.9 Critical EPSS 0.8% · p56
Should you act?
Critical, preconditions apply
Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- 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.
From the GitHub advisory
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
Mautic strongly recommend upgrading to a patched version immediately.
Weakness type: CWE-1336.
Product: mautic/core (Composer (PHP)) · Assigned by: Mautic · Published: 2026-05-29
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Composer (PHP) | mautic/core | >= 1.3.0, < 4.4.13 | none listed |
| Composer (PHP) | mautic/core | >= 5.0.0, < 5.2.11 | 5.2.11 |
| Composer (PHP) | mautic/core | >= 6.0.0, < 6.0.9 | 6.0.9 |
| Composer (PHP) | mautic/core | >= 7.0.0, < 7.1.2 | 7.1.2 |
| Vendor | Product | Affected versions (per 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 scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| Mautic | 3.1 | 9.9 Critical | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H |
| GitHub | 3.1 | 9.9 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: low (any account)
- User interaction: none
- Scope: changed (can affect other components)
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- 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.
Timeline
- — CVE record last updated
- — CVE record published by Mautic
- — GitHub-reviewed advisory GHSA-9fx4-7cmj-47vg published (critical)
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-9fx4-7cmj-47vg github.com
- CVE.org record CVE-2026-9558 cve.org
- NVD entry CVE-2026-9558 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
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