CVE-2020-26293 Possible XSS bypass if style tag is allowed
Attackers can execute scripts via crafted HTML if the style tag is explicitly allowed in HtmlSanitizer, requiring an upgrade to fix.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2020-26293?
CVE-2020-26293 is a medium-severity cross-site scripting vulnerability in mganss HtmlSanitizer, published on 4 Jan 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Which versions are affected by CVE-2020-26293?
2 open source packages ship an affected version, including HtmlSanitizer. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
HtmlSanitizer NuGet | All versions | 5.0.372 |
HtmlSanitizer NuGet | All versions | 5.0.372 |
Products include Htmlsanitizer Project Htmlsanitizer.
How do I fix CVE-2020-26293?
Upgrade HtmlSanitizer to 5.0.372 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2020-26293 being exploited?
There is no known exploitation of CVE-2020-26293 in the wild and no public exploit code.
Other vulnerabilities in mganss HtmlSanitizer
Sources
Also known as GHSA-8j9v-h2vp-2hhv.