---
id: "CVE-2026-117928"
kind: "vulnerability"
aliases: ["CVE-2026-117928"]
title: "Firefox: CSS parsing flaw lets pages bypass same-origin policy"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["desktop", "enterprise-esr", "firefox", "runtime"]
not_affected_if: ["firefox-159-or-later", "firefox-esr-153.6-or-later"]
published_at: "2026-10-27T14:16:48+00:00"
first_seen_at: "2026-10-27T14:32:23+00:00"
updated_at: "2026-10-27T14:37:11+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117928", "first_seen_at": "2026-10-27T14:32:23+00:00"}]
---

# Firefox: CSS parsing flaw lets pages bypass same-origin policy

A flaw in how Firefox parses and computes CSS lets content break the same-origin policy that keeps one site from reading another site's data. The sources do not say what an attacker can read or how reliably it can be used.

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

## How to check

- Check the Firefox version with Help > About Firefox or `firefox --version`; the fix is in Firefox 159 and Firefox ESR 153.6.
- Check the ESR line in use if the browser is managed by an enterprise policy.

## 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-2026-117928

## From the sources

Same-origin policy bypass in the CSS Parsing and Computation 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_