Affects widely deployed Mozilla Firefox/ESR; sandbox escape via WebRender could enable large-scale compromise of user hosts and enterprise endpoints.
CVE-2026-100797
Use-after-free in Firefox WebRender allows privilege escalation; fixed in recent Firefox/ESR.
Is CVE-2026-100797 being exploited?
Not confirmed. CVE-2026-100797 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.
How severe is CVE-2026-100797?
CVE-2026-100797 is rated High with a CVSS score of 8.8. 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-2026-100797?
Yes. A fix has been recorded for CVE-2026-100797. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100797 affect?
CVE-2026-100797 affects Mozilla Firefox (Desktop) - versions prior to fixes, Firefox 157 (fixed), Firefox ESR 153.4 (fixed), Firefox ESR 115.42 (fixed), and 1 further product or version. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-100797?
Update Firefox/ESR to the listed fixed versions immediately and enforce updates.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Local privilege escalation via use-after-free in WebRender; can escape browser sandbox and elevate attacker to higher OS privileges.
Patch when possible