CVE-2024-35218 is a medium-severity (CVSS 4.2) Cross-site Scripting (XSS) vulnerability in UmbracoCms.Core. A fix is available for UmbracoCms.Core — see the affected versions and patch details below.
Umbraco CMS Vulnerable to Stored XSS on Content Page Through Markdown Editor Preview Pane
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2024-35218.
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-2024-35218 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 377,238 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
UmbracoCms.Core.NETUmbracoCms.Core.NETUmbracoCms.Core.NETUmbracoCms.CoreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Umbraco CMS is an ASP.NET CMS used by more than 730.000 websites. Stored Cross-site scripting (XSS) enable attackers that have access to backoffice to bring malicious content into a website or application. This vulnerability has been patched in version(s) 8.18.13, 10.8.4, 12.3.7, 13.1.1 by implementing IHtmlSanitizer.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | UmbracoCms.Core | ≥ 8.0.0&&< 8.18.13 | 8.18.13dotnet add package UmbracoCms.Core --version 8.18.13 |
| .NETNuGet | UmbracoCms.Core | ≥ 10.0.0&&< 10.8.4 | 10.8.4dotnet add package UmbracoCms.Core --version 10.8.4 |
| .NETNuGet | UmbracoCms.Core | ≥ 12.0.0&&< 12.3.7 | 12.3.7dotnet add package UmbracoCms.Core --version 12.3.7 |
| .NETNuGet | UmbracoCms.Core | ≥ 13.0.0&&< 13.1.1 | 13.1.1dotnet add package UmbracoCms.Core --version 13.1.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for UmbracoCms.Core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update UmbracoCms.Core to 8.18.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-35218 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-2024-35218 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2024-35218. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2024-35218 in your dependencies?
O3 Security finds CVE-2024-35218 across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.