---
id: "CVE-2026-117891"
kind: "vulnerability"
aliases: ["CVE-2026-117891"]
title: "Firefox: JavaScript JIT use-after-free could let a web page run code"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["browsers", "desktop", "firefox", "runtime"]
not_affected_if: []
published_at: "2026-10-27T14:16:44+00:00"
first_seen_at: "2026-10-27T14:32:22+00:00"
updated_at: "2026-10-27T14:37:48+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117891", "first_seen_at": "2026-10-27T14:32:22+00:00"}]
---

# Firefox: JavaScript JIT use-after-free could let a web page run code

A use-after-free bug in the JIT compiler of Firefox's JavaScript engine lets memory be reused after it is freed. Per the sources, it was fixed in Firefox 159 and Firefox ESR 115.44 and 153.6, and the sources do not say what an attacker gets beyond that memory-safety flaw.

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

## How to check

- Run `firefox --version` (or check About Firefox) and compare against `159` for Firefox or `115.44` / `153.6` for the ESR branches
- unknown for any other check, as the sources do not say which configurations are exposed

## Fix

- Update Firefox to `159` or later
- Update Firefox ESR to `115.44` or `153.6` or later

## Timeline

- 2026-10-27T14:32:22+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-117891

## From the sources

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

---

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