CVE-2026-8956
Critical integer overflow in Mozilla Networking: JAR; patched in Firefox 151/Thunderbird 151.
Is CVE-2026-8956 being exploited?
Not confirmed. CVE-2026-8956 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 0.60% probability of exploitation in the next 30 days.
How severe is CVE-2026-8956?
CVE-2026-8956 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-2026-8956?
Yes. A fix has been recorded for CVE-2026-8956. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-8956 affect?
CVE-2026-8956 affects Mozilla Firefox 151, Firefox ESR 140.11, Mozilla Thunderbird 151, Thunderbird 140.11. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-8956?
Update to patched versions (Firefox 151 / ESR 140.11, Thunderbird 151 / 140.11)
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution via crafted network input causing memory corruption in the Networking: JAR component.
Patch when possible