---
id: "CVE-2026-117920"
kind: "vulnerability"
aliases: ["CVE-2026-117920"]
title: "Firefox: use-after-free in HTML parser can crash or run code"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["browsers", "desktop", "firefox", "runtime"]
not_affected_if: ["up-to-date-firefox"]
published_at: "2026-10-27T14:16:47+00:00"
first_seen_at: "2026-10-27T14:32:22+00:00"
updated_at: "2026-10-27T14:37:19+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117920", "first_seen_at": "2026-10-27T14:32:22+00:00"}]
---

# Firefox: use-after-free in HTML parser can crash or run code

A use-after-free bug in the DOM HTML Parser component of Firefox was fixed in Firefox 159 and Firefox ESR 153.6. Freed memory being reused can crash the browser or, in the worst case, let a crafted web page run code.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed Firefox version (Help > About Firefox) or run `firefox --version`
- unknown for other checks, the sources do not say

## Fix

- Update Firefox to `159` or later
- Update Firefox ESR to `153.6` or later

## Timeline

- 2026-10-27T14:32:22+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-117920

## From the sources

Use-after-free in the DOM: HTML Parser component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.

---

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