# CVE-2026-74979: Mozilla Firefox Add-ons Manager mitigation bypass

Source: https://junglewise.ai/threats/cve-2026-74979-mozilla-firefox-add-ons-manager-mitigation-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-18. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-74979 · Severity: critical · CVSS 9.8 · Published 2026-08-18

Firefox's Add-ons Manager contains a security mitigation that can be bypassed by an attacker with network access, potentially allowing them to circumvent protections designed to prevent malicious extensions from being installed or executed. This could enable unauthorized code execution within the browser context and compromise user data and system security.

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

## Quick answers

**Is CVE-2026-74979 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-74979 being exploited in the wild.

**How severe is CVE-2026-74979?** Critical severity, with a CVSS score of 9.8, published 18 August 2026.

**Which products and versions are affected?** Mozilla Firefox before 154; Mozilla Firefox ESR before 153.1; Mozilla Thunderbird before 153.1.

**Is there a fix for CVE-2026-74979?** A patch was published on 2026-08-18: Fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-74979 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-74979?** Check whether you run Mozilla Firefox, Mozilla Firefox ESR or Mozilla Thunderbird 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.

## Technical details

This is a mitigation bypass vulnerability in Firefox's Add-ons Manager component (CVE-2026-74979). The vulnerability allows an attacker to circumvent security mechanisms that protect against malicious extension installation or execution. The flaw is exploitable over the network without requiring user authentication or special privileges. The vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

## Affected products

- Mozilla Firefox before 154
- Mozilla Firefox ESR before 153.1
- Mozilla Thunderbird before 154
- Mozilla Thunderbird before 153.1

## Timeline

- 2026-08-18: disclosed: Publicly disclosed
- 2026-08-18: patched: Fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2045676](https://bugzilla.mozilla.org/show_bug.cgi?id=2045676)
- [https://www.mozilla.org/security/advisories/mfsa2026-74/](https://www.mozilla.org/security/advisories/mfsa2026-74/)

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