# Prototype Pollution in highlight.js

Advisory record · `GHSA-vfrc-7r7c-w9mx`

- **Identifiers:** `GHSA-vfrc-7r7c-w9mx` · `CVE-2020-26237`
- **State:** Confirmed
- **Severity:** CVSS 5.8 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-471](https://cwe.mitre.org/data/definitions/471.html)
- **Tags:** [CWE-471](https://agentprime.io/advisories/tag/cwe-471.md)
- **Published:** 24 Nov 2020
- **Updated:** 8 Jul 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 24 Nov 2020, 22:58 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `highlight.js` (npm): affected `<9.18.2 || >=10.0.0, <10.1.2`; fixed in `9.18.2`, `10.1.2`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 5.8 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:N/I:H/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.013, the 71st percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

This record came from the full history of the GitHub Advisory Database, published 24 Nov 2020. New records show when each source confirmed them.

## Sources

- [GitHub Advisory Database: GHSA-vfrc-7r7c-w9mx](https://github.com/advisories/GHSA-vfrc-7r7c-w9mx)
- [OSV: GHSA-vfrc-7r7c-w9mx](https://osv.dev/vulnerability/GHSA-vfrc-7r7c-w9mx)
- <https://github.com/highlightjs/highlight.js/security/advisories/GHSA-vfrc-7r7c-w9mx>
- <https://nvd.nist.gov/vuln/detail/CVE-2020-26237>
- <https://github.com/highlightjs/highlight.js/pull/2636>
- <https://github.com/highlightjs/highlight.js/commit/7241013ae011a585983e176ddc0489a7a52f6bb0>
- <https://github.com/highlightjs/highlight.js>
- <https://lists.debian.org/debian-lts-announce/2020/12/msg00041.html>
- <https://www.npmjs.com/package/highlight.js>
- <https://www.oracle.com/security-alerts/cpujul2022.html>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-vfrc-7r7c-w9mx>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-vfrc-7r7c-w9mx/>. Everything for agents: <https://agentprime.io/llms.txt>.