CVE-2021-41749 is a critical-severity (CVSS 9.8) Code Injection vulnerability in nystudio107/craft-seomatic. EPSS puts its 30-day exploitation probability at 18.1% (97th percentile). A fix is available for nystudio107/craft-seomatic — see the affected versions and patch details below.
Code Injection in SEOmatic
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-41749 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
nystudio107/craft-seomaticReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
In the SEOmatic plugin up to 3.4.11 for Craft CMS 3, it is possible for unauthenticated attackers to perform a Server-Side Template Injection, allowing for remote code execution.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | nystudio107/craft-seomatic | all versions | 3.4.11composer require nystudio107/craft-seomatic:^3.4.11 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nystudio107/craft-seomatic, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nystudio107/craft-seomatic to 3.4.11 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41749 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-41749 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-41749. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
How to detect CVE-2021-41749
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2021-41749 -u https://target- Template
- CraftCMS SEOmatic - Server-Side Template Injection
- Severity
- critical
- Impact
- Unauthenticated attackers can exploit SSTI via X-Forwarded-Host header to execute arbitrary Twig templates and system commands, achieving complete server compromise.
- Remediation
- Upgrade to CraftCMS SEOmatic version 3.4.12 or later.
Template by ProjectDiscovery nuclei-templates (iamnoooob, ritikchaddha), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2021-41749 in your dependencies?
O3 Security finds CVE-2021-41749 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.