Browser sandbox escape in Firefox allows remote arbitrary code execution on endpoints; Firefox is widely used across organizations and requires immediate action.
CVE-2026-100819
Firefox XPCOM sandbox escape enabling remote code execution.
Is CVE-2026-100819 being exploited?
Not confirmed. CVE-2026-100819 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.26% probability of exploitation in the next 30 days.
How severe is CVE-2026-100819?
CVE-2026-100819 is rated Critical with a CVSS score of 9.6. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-100819?
Yes. A fix has been recorded for CVE-2026-100819. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100819 affect?
CVE-2026-100819 affects Mozilla Firefox (desktop) prior to 157, Firefox ESR prior to 153.4, Firefox ESR prior to 140.17, Firefox ESR prior to 115.42. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-100819?
Upgrade Firefox/ESR to the listed fixed versions immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Sandbox escape via XPCOM lets an attacker execute arbitrary code on a victim's host through crafted web content.
Immediate action required