CVE-2026-84637
Thunderbird calendar invites can launch local or network executables via file:// attachments.
Is CVE-2026-84637 being exploited?
Not confirmed. CVE-2026-84637 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 0.34% probability of exploitation in the next 30 days.
How severe is CVE-2026-84637?
CVE-2026-84637 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-2026-84637?
Yes. A fix has been recorded for CVE-2026-84637. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-84637 affect?
CVE-2026-84637 affects Mozilla Thunderbird (calendar/invite component) — versions before 154 and before 153.2. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-84637?
Update Thunderbird to 154 or 153.2 immediately; block/untrust calendar invites until patched.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attackers can execute local or network-hosted executables via malicious calendar invites, bypassing attachment protections and running code as the user.
Immediate action required