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Prototype Pollution in highlight.js

low severity Published Nov 24, 2020 in highlightjs/highlight.js • Updated Jan 8, 2021

Package

npm highlight.js (npm)

Affected versions

< 9.18.2
>= 10.0.0, < 10.1.2

Patched versions

9.18.2
10.1.2

Description

Impact

Affected versions of this package are vulnerable to Prototype Pollution. A malicious HTML code block can be crafted that will result in prototype pollution of the base object's prototype during highlighting. If you allow users to insert custom HTML code blocks into your page/app via parsing Markdown code blocks (or similar) and do not filter the language names the user can provide you may be vulnerable.

The pollution should just be harmless data but this can cause problems for applications not expecting these properties to exist and can result in strange behavior or application crashes, i.e. a potential DOS vector.

If your website or application does not render user provided data it should be unaffected.

Patches

Versions 9.18.2 and 10.1.2 and newer include fixes for this vulnerability. If you are using version 7 or 8 you are encouraged to upgrade to a newer release.

Workarounds

Patch your library

Manually patch your library to create null objects for both languages and aliases:

const HLJS = function(hljs) {
  // ...
  var languages = Object.create(null);
  var aliases = Object.create(null);

Filter out bad data from end users

Filter the language names that users are allowed to inject into your HTML to guarantee they are valid.

References

For more information

If you have any questions or comments about this advisory:

References

@joshgoebel joshgoebel published the maintainer security advisory Nov 24, 2020

CVE ID

CVE-2020-26237

CVSS Score

5.8 Moderate
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:N/I:H/A:N

Credits