# CVE-2026-124939: Mozilla Firefox JIT miscompilation in JavaScript Engine

Source: https://junglewise.ai/threats/cve-2026-124939-jit-miscompilation-in-the-javascript-engine-jit-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-2026-124939 · Severity: info · Published 2026-11-10

Firefox's JavaScript JIT compiler contained a miscompilation flaw that could allow attackers to execute arbitrary code through specially crafted scripts. This vulnerability affects Firefox users browsing untrusted websites, potentially leading to account compromise, malware installation, or data theft. Mozilla has released fixes 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-2026-124939 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-124939 being exploited in the wild.

**How severe is CVE-2026-124939?** 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-2026-124939?** 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-2026-124939 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-124939?** 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 miscompilation bug in the JIT (Just-In-Time) component of Firefox's JavaScript engine could generate incorrect machine code, allowing an attacker to bypass security checks or achieve code execution through malicious JavaScript. The vulnerability requires no user authentication and affects all Firefox versions prior to the patched releases. No known active exploitation has been reported.

## Affected products

- Mozilla Firefox before 160
- Mozilla Firefox ESR before 153.7

## Timeline

- 2026-11-10: disclosed

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2076663](https://bugzilla.mozilla.org/show_bug.cgi?id=2076663)
- [https://www.mozilla.org/security/advisories/mfsa2026-125/](https://www.mozilla.org/security/advisories/mfsa2026-125/)

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