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9.8 Critical

CVE-2026-16387 Site isolation issue in the Networking component

Description

Site isolation issue in the Networking component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

Affected products and versions

Product	Affected versions	Fixed in
Firefox 153	earliest → < 153	153
Firefox 140.13	earliest → < 140.13	140.13
Thunderbird 153	earliest → < 153	153
Thunderbird 140.13	earliest → < 140.13	140.13

References

bugzilla.mozilla.org bugzilla.mozilla.org
www.mozilla.org www.mozilla.org
www.mozilla.org www.mozilla.org
www.mozilla.org www.mozilla.org
www.mozilla.org www.mozilla.org

Timeline

Published July 21, 2026
Last modified July 22, 2026

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