---
id: "CVE-2026-117870"
kind: "vulnerability"
aliases: ["CVE-2026-117870"]
title: "Firefox: use-after-free in JavaScript engine fixed in version 159"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["browsers", "desktop", "firefox", "runtime"]
not_affected_if: ["already-on-fixed-version"]
published_at: "2026-10-27T14:16:41+00:00"
first_seen_at: "2026-10-27T14:32:21+00:00"
updated_at: "2026-10-27T14:39:15+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117870", "first_seen_at": "2026-10-27T14:32:21+00:00"}]
---

# Firefox: use-after-free in JavaScript engine fixed in version 159

A use-after-free bug in the JavaScript Engine component of Firefox was fixed in Firefox 159, Firefox ESR 115.44, and Firefox ESR 153.6. The sources do not state what an attacker can do with it beyond the memory-corruption class.

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

## How to check

- Check the installed Firefox version in the browser's About page or with `firefox --version`.
- Compare against the fixed releases: `159`, `115.44`, and `153.6`.

## Fix

- Update Firefox to `159` or later.
- Update Firefox ESR to `115.44` or `153.6` on the ESR branch in use.

## Timeline

- 2026-10-27T14:32:21+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-117870

## From the sources

Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 159, Firefox ESR 115.44, and Firefox ESR 153.6.

---

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