---
id: "CVE-2026-118021"
kind: "vulnerability"
aliases: ["CVE-2026-118021"]
title: "Firefox: use-after-free in XPCOM lets web content escape the sandbox"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["browsers", "desktop", "firefox", "runtime"]
not_affected_if: ["firefox-159-or-later"]
published_at: "2026-10-27T14:16:59+00:00"
first_seen_at: "2026-10-27T14:32:25+00:00"
updated_at: "2026-10-27T14:33:23+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-118021", "first_seen_at": "2026-10-27T14:32:25+00:00"}]
---

# Firefox: use-after-free in XPCOM lets web content escape the sandbox

A use-after-free bug in Firefox's XPCOM component allows a sandbox escape. The sources do not say what an attacker gains beyond leaving the sandbox.

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

## How to check

- Run `firefox --version` or open About Firefox and compare against `159`
- Check the Firefox version bundled by your managed browser or deployment tooling; the sources do not name other affected versions

## Fix

- Update Firefox to `159` or later
- unknown for other products or ESR branches, the sources do not say

## Timeline

- 2026-10-27T14:32:25+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-118021

## From the sources

Sandbox escape due to use-after-free in the XPCOM component. This vulnerability was fixed in Firefox 159.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_