High-severity NSS integer overflow allows potential remote code execution in widely used Mozilla products (Firefox/Thunderbird); broad impact across organizations.
CVE-2026-16389
Integer overflow in NSS enabling potential remote code execution in Firefox/Thunderbird
Is CVE-2026-16389 being exploited?
Not confirmed. CVE-2026-16389 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 0.56% probability of exploitation in the next 30 days.
How severe is CVE-2026-16389?
CVE-2026-16389 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-2026-16389?
Yes. A fix has been recorded for CVE-2026-16389. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16389 affect?
CVE-2026-16389 affects NSS (Network Security Services), Mozilla Firefox <153, Mozilla Thunderbird <153, Applications using NSS. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-16389?
Upgrade Firefox/Thunderbird and NSS-based apps to version 153+ immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Crafted input triggers integer overflow in NSS leading to memory corruption and potential remote code execution or application crashes.
Immediate action required