RCE risk in NSS libraries affecting Firefox/Thunderbird; widely deployed across orgs and user bases.
CVE-2026-2781
RCE via NSS integer overflow in Firefox/Thunderbird
Is CVE-2026-2781 being exploited?
Not confirmed. CVE-2026-2781 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 0.36% probability of exploitation in the next 30 days.
How severe is CVE-2026-2781?
CVE-2026-2781 is rated Critical with a CVSS score of 9.8. 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-2026-2781?
Yes. A fix has been recorded for CVE-2026-2781. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-2781 affect?
CVE-2026-2781 affects Firefox < 148, Firefox ESR < 140.8, Thunderbird < 148, Thunderbird < 140.8. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-2781?
Update to latest Firefox/Thunderbird (>= 148/140.8)
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
RCE in Mozilla apps due to NSS overflow; attacker can run arbitrary code on affected hosts
Patch when possible