CVE-2026-117966
Low risk· EPSS 8%Exploitation Probability (EPSS)
Low risk8th percentile - higher than 8% of all known CVEs
Summary
A site isolation issue exists in the Networking: HTTP component of Firefox and Thunderbird. The vulnerability was fixed in Firefox 159, Firefox ESR 115.44, Firefox ESR 153.6, Thunderbird 159, and Thunderbird 153.6.
Risk Assessment
Weakened site isolation can allow access to data from other origins and bypass browser security mechanisms. The risk affects users visiting untrusted sites.
Recommendation
Update Firefox and Thunderbird to the fixed versions (Firefox 159, ESR 115.44, ESR 153.6, Thunderbird 159, 153.6). Prioritize systems used to browse untrusted websites.
Other vulnerabilities in Firefox
See all- CVE-2026-113470Medium
Mozilla blocked compromised intermediate eMudhra certificates via OneCRL on October 17, and the list was distributed to clients via RemoteSettings the same day. This update contains the updated OneCRL block list, ensuring clients will block the compromised certificates even if RemoteSettings is disabled by policy or otherwise unavailable in the user's network environment. The vulnerability was fixed in Firefox 158.0.1, Firefox ESR 153.5.1, Firefox ESR 115.43.1, Thunderbird 158.0.1, and Thunderbird 153.5.1.
- CVE-2026-113401Medium
A denial-of-service vulnerability exists in the PDF Viewer component. The vulnerability was fixed in Firefox 158.0.1 and Thunderbird 158.0.1.
- CVE-2026-109780Critical
Vulnerability in the DOM: Core & HTML component allows mitigation bypass. This issue was fixed in Firefox 158 and Thunderbird 158.
- CVE-2026-109774Critical
Invalid pointer and undefined behavior in the DOM: Notifications component. Fixed in Firefox 158 and Thunderbird 158.
- CVE-2026-109772Critical
Same-origin policy bypass in the DevTools component. Fixed in Firefox 158 and Thunderbird 158.
- CVE-2026-109755Critical
A vulnerability in the DOM: Content Processes component allows sandbox escape. It was fixed in Firefox 158 and Thunderbird 158.
- CVE-2026-109750Critical
A vulnerability in the DOM: Web Authentication component causes a site isolation issue. It was fixed in Firefox 158 and Thunderbird 158.
- CVE-2026-109745Critical
Sandbox escape due to uninitialized memory in the DOM: Web Serial component. It was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.
- CVE-2026-109740Critical
Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. The flaw was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.
- CVE-2026-106016Critical
Mitigation bypass in the File Handling component. This vulnerability was fixed in Firefox 157.0.1 and Thunderbird 158.
Original NVD description (English source)
Site isolation issue in the Networking: HTTP component. This vulnerability was fixed in Firefox 159, Firefox ESR 115.44, Firefox ESR 153.6, Thunderbird 159, and Thunderbird 153.6.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS