---
id: "CVE-2026-117958"
kind: "vulnerability"
aliases: ["CVE-2026-117958"]
title: "Firefox: site isolation flaw in HTTP networking fixed in 159"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "other"
products: []
ecosystems: []
tags: ["browser", "desktop", "firefox", "other"]
not_affected_if: ["not-running-firefox"]
published_at: "2026-10-27T14:16:51+00:00"
first_seen_at: "2026-10-27T14:32:23+00:00"
updated_at: "2026-10-27T14:35:31+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117958", "first_seen_at": "2026-10-27T14:32:23+00:00"}]
---

# Firefox: site isolation flaw in HTTP networking fixed in 159

A site isolation weakness in the Networking HTTP component of Firefox let one website interact with data from another site it should not reach. The sources do not say what data an attacker could read or how the flaw is triggered, and the description only states the fixed releases.

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

## How to check

- Check the installed Firefox version in the About Firefox dialog or with `firefox --version`, and compare it with the fixed releases.
- Check whether ESR installs are on `153.6` or later.

## Fix

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

## Timeline

- 2026-10-27T14:32:23+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-117958

## From the sources

Site isolation issue in the Networking: HTTP component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.

---

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