# CVE-2020-26237: libjs-highlight: Highlight.js is a syntax highlighter written in JavaScript

CVE-2020-26237 is fixed in 4 products on 1 platform, first by libjs-highlight 9.12.0+dfsg1-4ubuntu0.1~esm1, released November 24, 2020. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2020-26237
- Priority: Routine
- CVSS: n/a (Medium)
- EPSS: 0.0133
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Nov 24, 2020

## Description

Highlight.js is a syntax highlighter written in JavaScript. Highlight.js versions before 9.18.2 and 10.1.2 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. 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libjs-highlight Ubuntu 18.04.6 LTS (bionic) | 9.12.0+dfsg1-4ubuntu0.1~esm1 | [libjs-highlight 9.12.0+dfsg1-4ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libjs-highlight-9.12.0-dfsg1-4ubuntu0.1-esm1.md) | Nov 24, 2020 |
| Linux | libjs-highlight Ubuntu 20.04 LTS (focal) | 9.12.0+dfsg1-5ubuntu0.1~esm1 | [libjs-highlight 9.12.0+dfsg1-5ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libjs-highlight-9.12.0-dfsg1-5ubuntu0.1-esm1.md) | Nov 24, 2020 |
| Linux | libjs-highlight.js Ubuntu 18.04.6 LTS (bionic) | 9.12.0+dfsg1-4ubuntu0.1~esm1 | [libjs-highlight.js 9.12.0+dfsg1-4ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libjs-highlight.js-9.12.0-dfsg1-4ubuntu0.1-esm1.md) | Nov 24, 2020 |
| Linux | libjs-highlight.js Ubuntu 20.04 LTS (focal) | 9.12.0+dfsg1-5ubuntu0.1~esm1 | [libjs-highlight.js 9.12.0+dfsg1-5ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libjs-highlight.js-9.12.0-dfsg1-5ubuntu0.1-esm1.md) | Nov 24, 2020 |
| Linux | node-highlight Ubuntu 18.04.6 LTS (bionic) | 9.12.0+dfsg1-4ubuntu0.1~esm1 | [node-highlight 9.12.0+dfsg1-4ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-node-highlight-9.12.0-dfsg1-4ubuntu0.1-esm1.md) | Nov 24, 2020 |
| Linux | node-highlight Ubuntu 20.04 LTS (focal) | 9.12.0+dfsg1-5ubuntu0.1~esm1 | [node-highlight 9.12.0+dfsg1-5ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-node-highlight-9.12.0-dfsg1-5ubuntu0.1-esm1.md) | Nov 24, 2020 |
| Linux | node-highlight.js Ubuntu 18.04.6 LTS (bionic) | 9.12.0+dfsg1-4ubuntu0.1~esm1 | [node-highlight.js 9.12.0+dfsg1-4ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-node-highlight.js-9.12.0-dfsg1-4ubuntu0.1-esm1.md) | Nov 24, 2020 |
| Linux | node-highlight.js Ubuntu 20.04 LTS (focal) | 9.12.0+dfsg1-5ubuntu0.1~esm1 | [node-highlight.js 9.12.0+dfsg1-5ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-node-highlight.js-9.12.0-dfsg1-5ubuntu0.1-esm1.md) | Nov 24, 2020 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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