PatchTheCVEh2o vulnerabilities
Recent CVEs affecting h2o products. 4 tracked.
h2o has 4 tracked vulnerabilities, 0 critical. A fixed release or vendor patch exists for 4. Most recent: 2026-07-16. Highest priority: CVE-2026-44435 (score 42/100).
- CVE-2026-44435 HIGH 7.5 UPGRADE Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server
- CVE-2026-44436 HIGH 7.5 UPGRADE Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server
- CVE-2026-44433 MEDIUM 5.3 UPGRADE Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server
- CVE-2026-44434 MEDIUM 5.3 UPGRADE Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server
FAQ
How do I fix h2o vulnerabilities?
Open the CVE for your version, check the affected range, then follow the listed action: upgrade to the fixed release, or downgrade or mitigate if no fix exists yet. Commands for each OS are shown on every CVE page.
Is h2o being exploited right now?
None of the tracked h2o CVEs are on the CISA Known Exploited Vulnerabilities list at the moment. This is checked every 20 minutes.
Which h2o CVE should I patch first?
CVE-2026-44435 currently ranks highest (42/100): Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server.