---
id: "CVE-2026-117939"
kind: "vulnerability"
aliases: ["CVE-2026-117939"]
title: "Firefox: use-after-free in XML component fixed in version 159"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "other"
products: []
ecosystems: []
tags: ["browser", "desktop", "firefox", "other"]
not_affected_if: ["already-patched"]
published_at: "2026-10-27T14:16:49+00:00"
first_seen_at: "2026-10-27T14:32:23+00:00"
updated_at: "2026-10-27T14:37:01+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117939", "first_seen_at": "2026-10-27T14:32:23+00:00"}]
---

# Firefox: use-after-free in XML component fixed in version 159

Firefox has a use-after-free bug in its XML component, where memory is used after it has been released. The sources do not say what an attacker can do with it beyond that memory-safety flaw.

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

## How to check

- Check the installed Firefox version against the fixed releases: `159`, ESR `115.44`, and ESR `153.6`.
- unknown

## Fix

- Update Firefox to `159` or later.
- If on the ESR channel, update to `115.44` (ESR 115 line) or `153.6` (ESR 153 line).

## Timeline

- 2026-10-27T14:32:23+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-117939

## From the sources

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

---

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