CVE-2026-61666
WebSocket server crash via malformed Host header in websocket-driver (<0.8.2).
Is CVE-2026-61666 being exploited?
Not confirmed. CVE-2026-61666 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-2026-61666?
CVE-2026-61666 is rated High with a CVSS score of 8.9. 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-2026-61666?
Yes. A fix has been recorded for CVE-2026-61666. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-61666 affect?
CVE-2026-61666 affects websocket-driver Ruby gem <0.8.2, Ruby WebSocket servers using websocket-driver, Applications with TCP-backed WebSocket endpoints. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-61666?
Upgrade websocket-driver to >=0.8.2 and validate Host header parsing.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote Denial of Service: crafted Host header triggers unhandled URI::InvalidURIError, crashing TCP-backed WebSocket servers.
Patch when possible
- affected< 0.8.2
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.