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Firefox 159 Fixes 167 Security Vulnerabilities Including High-Risk Flaws

Firefox 159 Fixes 167 Security Vulnerabilities Including High-Risk Flaws

First seen 31 Oct 2026, 20:13 UTC • •
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ThreatCluster AI
ThreatCluster •October 31, 2026 at 21:42 UTC
  • •Firefox 159.0 fixes 167 vulnerabilities, including 108 high-risk issues.
  • •The update includes 13 vulnerabilities that could enable sandbox escapes.
  • •New features include a sidebar password tool and an AI-assisted Smart Window.

Mozilla released Firefox 159.0 on October 27, 2026, addressing 167 vulnerabilities rated from high to low. The update includes 108 high-risk vulnerabilities, 52 medium-risk, and 7 low-risk issues. Notably, 13 vulnerabilities could allow sandbox escapes, while 97 are categorized as use-after-free vulnerabilities. The update affects all major operating systems including Windows, macOS, Linux, and Android. External researchers reported 65 of these vulnerabilities, with Amy Burnett from OpenAI contributing seven reports. The release also introduces new features like a sidebar password tool and an AI-assisted Smart Window for monitoring website changes. Users are encouraged to update their browsers immediately to mitigate potential risks. Firefox ESR versions have also been updated to address vulnerabilities present in older browser generations.

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Timeline

2026-10-27
Firefox 159.0 released
Mozilla released Firefox 159.0, fixing 167 vulnerabilities across all major operating systems.
Neoteo
2026-10-27
Security Advisory 2026-118 published
Mozilla's advisory detailed 167 vulnerabilities fixed in Firefox 159, including high-risk issues.
Pcworld

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Common questions

What vulnerabilities were fixed in Firefox 159?
Firefox 159 fixed 167 vulnerabilities, including 108 high-risk and 13 sandbox escape vulnerabilities.
Which systems are affected by these vulnerabilities?
The vulnerabilities affect Firefox on Windows, macOS, Linux, and Android.
How can I update to Firefox 159?
Users can update by selecting Help > Firefox in the browser to check for and download the latest version.