HtmlSanitizer is a .NET library for cleaning HTML fragments and documents from constructs that can lead to XSS attacks. The vulnerability occurs in configurations where foreign content is allowed, i.e. either `svg` or `math` are in the list of allowed elements. In the case an application sanitizes user input with a vulnerable configuration, an attacker could bypass the sanitization and inject arbitrary HTML, including JavaScript code. Note that in the default configuration the vulnerability is not present. The vulnerability has been fixed in versions 8.0.723 and 8.1.722-beta (preview version).

Affected: NuGet: HtmlSanitizer

### Impact

The vulnerability occurs in configurations where foreign content is allowed, i.e. either `svg` or `math` are in the list of allowed elements. Specifically, the requirements for the vulnerability are:

1. Allowing one foreign element: `svg`, or `math` 2. Comments or one raw text element: `iframe`, `noembed`, `xmp`, `title`, `noframes`, `style` or `noscript`

Configurations that meet the above requirements plus the following are vulnerable to an additional vulnerability:

- Any HTML integration element: `title`, `desc`, `mi`, `mo`, `mn`, `ms`, `mtext`, `annotation-xml`.

In case an application sanitizes user input with a vulnerable configuration, an attacker could bypass the sanitization and inject arbitrary HTML, including JavaScript code.

Note that in the default configuration the vulnerability is not present.

### Patches

The vulnerability has been fixed in versions 8.0.723 and 8.1.722-beta (preview version).

### Workarounds

Disallow foreign elements `svg` and `math`. This is the case in the default configuration, which is therefore not affected by the vulnerability.