CVE-2026-55367High· 7.5▾ Twilighth2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 4212ce114506a073505fd389db16ad2ba4e582a0, a client could send an incomplete CONNECT-UDP Capsule with an excessively large declared length, causing H2O to…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 41.3 · likelihood 0.1 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake. The CVSS score shown above comes from the assigning CNA record, not NVD.
Exploit-prediction probability, daily snapshots since Nov 5.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
Last analysed / modified upstream
0.3%
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 4212ce114506a073505fd389db16ad2ba4e582a0, a client could send an incomplete CONNECT-UDP Capsule with an excessively large declared length, causing H2O to keep buffering received bytes without a per-Capsule limit while waiting for the remainder. Deployments that enabled proxy.connect-udp and accepted CONNECT-UDP requests could exhaust server memory and lose availability. This vulnerability is fixed with commit 4212ce114506a073505fd389db16ad2ba4e582a0.
h2o < 4212ce114506a073505fd389db16ad2ba4e582a0Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Connected by shared product, vendor, weakness, or advisory.
CVE-2026-55368High· 8.1h2o: buffer overflow when using the %{error}x log directive
CVE-2023-6569Critical· 9.3External Control of File Name or Path in h2oai/h2o-3
CVE-2024-10553Critical· 9.8H2O Deserialization of Untrusted Data Vulnerability
CVE-2026-8752Medium· 5.3A weakness has been identified in h2oai h2o-3 up to 7402
CVE-2026-8750Medium· 5.3A vulnerability was identified in h2oai h2o-3 up to 7402
CVE-2026-8751High· 7.3A security flaw has been discovered in h2oai h2o-3 up to 7402