CVE-2020-26293
MEDIUMCVE-2020-26293 is a medium-severity (CVSS 6.1) CWE-74 vulnerability in HtmlSanitizer. O3 Security confirms whether CVE-2020-26293 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
XSS in HtmlSanitizer
Blast Radius
HtmlSanitizerReal-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
HtmlSanitizer is a .NET library for cleaning HTML fragments and documents from constructs that can lead to XSS attacks. In HtmlSanitizer before version 5.0.372, there is a possible XSS bypass if style tag is allowed. If you have explicitly allowed the <style> tag, an attacker could craft HTML that includes script after passing through the sanitizer. The default settings disallow the <style> tag so there is no risk if you have not explicitly allowed the <style> tag. The problem has been fixed in version 5.0.372.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | HtmlSanitizer | all versions | 5.0.372 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for HtmlSanitizer. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update HtmlSanitizer to 5.0.372 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-26293 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 pinpoints whether CVE-2020-26293 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2020-26293. 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-2020-26293 in your dependencies?
O3 detects CVE-2020-26293 across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.