# CVE-2026-124931: Firefox same-origin policy bypass in DOM: Core & HTML

Source: https://junglewise.ai/threats/cve-2026-124931-same-origin-policy-bypass-in-the-dom-core-html-component-this  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-10. Updated: 2026-11-10  
License: CC BY 4.0 with a link back

CVE-2026-124931 · Severity: info · Published 2026-11-10

Firefox, a web browser used by millions to access the internet securely, contains a flaw in how it enforces the same-origin policy—a critical security boundary that prevents websites from accessing each other's data. An attacker could exploit this to steal sensitive information from other websites or sessions the user has open. This issue has been fixed in Firefox 160 and Firefox ESR 153.7.

Technologies: [Mozilla Firefox](https://junglewise.ai/threats/technologies/firefox), [Mozilla Firefox ESR](https://junglewise.ai/threats/technologies/firefox-esr). Vendors: [Mozilla](https://junglewise.ai/threats/vendors/mozilla).

## Quick answers

**Is CVE-2026-124931 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-124931 being exploited in the wild.

**How severe is CVE-2026-124931?** Informational severity, published 10 November 2026.

**Which products and versions are affected?** Mozilla Firefox before 160; Mozilla Firefox ESR before 153.7.

**Is there a fix for CVE-2026-124931?** Yes: fixed in Firefox 160, Firefox ESR 153.7. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-124931 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-124931?** Check whether you run Mozilla Firefox or Mozilla Firefox ESR at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in Firefox 160, Firefox ESR 153.7

## Technical details

A same-origin policy bypass vulnerability exists in Firefox's DOM: Core & HTML component, allowing an attacker to access data or resources from different origins that should be restricted. The vulnerability is triggered through normal web browsing (network attack vector) without requiring authentication or special user interaction. Successful exploitation permits unauthorized cross-origin data access, compromising the browser's fundamental security model.

## Affected products

- Mozilla Firefox before 160
- Mozilla Firefox ESR before 153.7

## Timeline

- 2026-11-10: disclosed
- 2026-11-10: patched

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2083990](https://bugzilla.mozilla.org/show_bug.cgi?id=2083990)
- [https://www.mozilla.org/security/advisories/mfsa2026-125/](https://www.mozilla.org/security/advisories/mfsa2026-125/)

## Related threats

- [Firefox ESR use-after-free in Audio/Video component](https://junglewise.ai/threats/cve-2026-124952-use-after-free-in-the-audio-video-component-this-vulnerability)
- [Firefox privilege escalation in Nimbus Desktop Client](https://junglewise.ai/threats/cve-2026-124951-privilege-escalation-in-the-nimbus-desktop-client-component-this)
- [Firefox same-origin policy bypass in CSS Parsing and Computation](https://junglewise.ai/threats/cve-2026-124950-same-origin-policy-bypass-in-the-css-parsing-and-computation)
- [Firefox other issue in SVG component](https://junglewise.ai/threats/cve-2026-124949-other-issue-in-the-svg-component-this-vulnerability-was-fixed-in)
- [Mozilla Firefox use-after-free in Graphics component](https://junglewise.ai/threats/cve-2026-124948-incorrect-boundary-conditions-use-after-free-in-the-graphics)