Summary
XSS in HtmlSanitizer
Workarounds
Remove the <style> tag from the set of allowed tags.
For more information
If you have any questions or comments about this advisory open an issue in https://github.com/mganss/HtmlSanitizer
Credits
This issue was discovered by Michal Bentkowski of Securitum.
Impact
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.
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2020-26293 has a CVSS score of 6.1 (Low). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.0.372); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
The problem has been fixed in version 5.0.372.
Frequently Asked Questions
- What is CVE-2020-26293? CVE-2020-26293 is a low-severity cross-site scripting (XSS) vulnerability in HtmlSanitizer (nuget), affecting versions < 5.0.372. It is fixed in 5.0.372. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2020-26293? CVE-2020-26293 has a CVSS score of 6.1 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of HtmlSanitizer are affected by CVE-2020-26293? HtmlSanitizer (nuget) versions < 5.0.372 is affected.
- Is there a fix for CVE-2020-26293? Yes. CVE-2020-26293 is fixed in 5.0.372. Upgrade to this version or later.
- Is CVE-2020-26293 exploitable, and should I be worried? Whether CVE-2020-26293 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2020-26293 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2020-26293? Upgrade
HtmlSanitizerto 5.0.372 or later.