XSS in HtmlSanitizer

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N

EPSS

• CVE-2020-26293: 1.01% estimated exploitation activity in the next 30 days; percentile 63.15 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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. Patches The problem has been fixed in version 5.0.372. 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.

Published by the source

4 Jan 2021, 18:22 UTC

Last modified by the source

1 Feb 2023, 05:05 UTC

Source last checked

26 Oct 2026, 16:59 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-8j9v-h2vp-2hhv

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# Patch Next advisory brief: CVE-2020-26293

Advisory: XSS in HtmlSanitizer
IDs: CVE-2020-26293, GHSA-8j9v-h2vp-2hhv
Record: https://patchnext.com/advisories/cve-2020-26293 (revision 1, source checked 26 Oct 2026, 16:59 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: htmlsanitizer 5.0.372. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet htmlsanitizer: affected < 5.0.372; fixed in 5.0.372

## Suggested inspection (read-only)
- NuGet htmlsanitizer: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on htmlsanitizer.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-8j9v-h2vp-2hhv (GitHub-reviewed advisory GHSA-8j9v-h2vp-2hhv lists affected ranges: NuGet htmlsanitizer >=0 <5.0.372)

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