# H2o vulnerabilities Source: https://junglewise.ai/threats/vendors/h2o Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats Updated: 12 November 2026, 03:07 UTC. Rebuilt every hour. Data: https://junglewise.ai/threats/vendors/h2o.json License: CC BY 4.0 with a link back Junglewise Threat Intelligence has tracked 9 vulnerabilities in H2o: 0 in the last 7 days and 4 in the last 90 days, 0 of them critical and 0 exploited in the wild. The most recent, CVE-2026-55368, was published on 4 November 2026. 3 vulnerabilities in the last four weeks, up from none in the four before. 1 technology has a page of its own. ## Counts - Last 7 days: 0 - Last 30 days: 3 - Last 90 days: 4 - All time: 9 (0 critical, 0 exploited in the wild) ## About H2o A software vendor that develops the H2O open-source distributed machine learning platform. ## Latest H2o vulnerabilities - [CVE-2026-55368: H2O HTTP server buffer overflow in access-log formatter](https://junglewise.ai/threats/cve-2026-55368-h2o-is-an-http-server-with-support-for-http-1-x-http-2-and-http-3) (high, CVSS 8.1, published 4 Nov 2026) - [CVE-2026-55367: h2o HTTP server denial of service in CONNECT-UDP parsing](https://junglewise.ai/threats/cve-2026-55367-h2o-is-an-http-server-with-support-for-http-1-x-http-2-and-http-3) (high, CVSS 7.5, published 4 Nov 2026) - [CVE-2026-59993: Picotls null pointer dereference in TLS client handshake](https://junglewise.ai/threats/cve-2026-59993-picotls-is-a-tls-protocol-library-that-allows-users-select) (medium, CVSS 6.5, published 30 Oct 2026) - [CVE-2026-45271: Picotls ASN.1 decoder stack exhaustion](https://junglewise.ai/threats/cve-2026-45271-picotls-asn-1-decoder-stack-exhaustion) (medium, CVSS 5.5, published 21 Aug 2026) - [CVE-2026-44436: h2o Quicly denial of service via Connection ID buffer overflow](https://junglewise.ai/threats/cve-2026-44436-h2o-quicly-denial-of-service-via-connection-id-buffer-overflow) (high, CVSS 7.5, published 16 Jul 2026) - [CVE-2026-44435: H2O Quicly assertion failure in CRYPTO stream handling](https://junglewise.ai/threats/cve-2026-44435-h2o-quicly-assertion-failure-in-crypto-stream-handling) (high, CVSS 7.5, published 16 Jul 2026) - [CVE-2026-44434: h2o Quicly stateless reset injection in lib/quicly.c](https://junglewise.ai/threats/cve-2026-44434-h2o-quicly-stateless-reset-injection-in-lib-quicly-c) (medium, CVSS 5.3, published 16 Jul 2026) - [CVE-2026-44433: h2o quicly resource exhaustion in flow control credit management](https://junglewise.ai/threats/cve-2026-44433-h2o-quicly-resource-exhaustion-in-flow-control-credit-management) (medium, CVSS 5.3, published 16 Jul 2026) - [CVE-2026-55213: h2o stack overflow in QPACK HTTP/3 processing](https://junglewise.ai/threats/cve-2026-55213-h2o-stack-overflow-in-qpack-http-3-processing) (high, CVSS 7.5, published 10 Jul 2026) ## Most severe H2o vulnerabilities - [CVE-2026-55368: H2O HTTP server buffer overflow in access-log formatter](https://junglewise.ai/threats/cve-2026-55368-h2o-is-an-http-server-with-support-for-http-1-x-http-2-and-http-3) (high, CVSS 8.1, published 4 Nov 2026) - [CVE-2026-55367: h2o HTTP server denial of service in CONNECT-UDP parsing](https://junglewise.ai/threats/cve-2026-55367-h2o-is-an-http-server-with-support-for-http-1-x-http-2-and-http-3) (high, CVSS 7.5, published 4 Nov 2026) - [CVE-2026-44436: h2o Quicly denial of service via Connection ID buffer overflow](https://junglewise.ai/threats/cve-2026-44436-h2o-quicly-denial-of-service-via-connection-id-buffer-overflow) (high, CVSS 7.5, published 16 Jul 2026) - [CVE-2026-44435: H2O Quicly assertion failure in CRYPTO stream handling](https://junglewise.ai/threats/cve-2026-44435-h2o-quicly-assertion-failure-in-crypto-stream-handling) (high, CVSS 7.5, published 16 Jul 2026) - [CVE-2026-55213: h2o stack overflow in QPACK HTTP/3 processing](https://junglewise.ai/threats/cve-2026-55213-h2o-stack-overflow-in-qpack-http-3-processing) (high, CVSS 7.5, published 10 Jul 2026) - [CVE-2026-59993: Picotls null pointer dereference in TLS client handshake](https://junglewise.ai/threats/cve-2026-59993-picotls-is-a-tls-protocol-library-that-allows-users-select) (medium, CVSS 6.5, published 30 Oct 2026) - [CVE-2026-45271: Picotls ASN.1 decoder stack exhaustion](https://junglewise.ai/threats/cve-2026-45271-picotls-asn-1-decoder-stack-exhaustion) (medium, CVSS 5.5, published 21 Aug 2026) - [CVE-2026-44434: h2o Quicly stateless reset injection in lib/quicly.c](https://junglewise.ai/threats/cve-2026-44434-h2o-quicly-stateless-reset-injection-in-lib-quicly-c) (medium, CVSS 5.3, published 16 Jul 2026) - [CVE-2026-44433: h2o quicly resource exhaustion in flow control credit management](https://junglewise.ai/threats/cve-2026-44433-h2o-quicly-resource-exhaustion-in-flow-control-credit-management) (medium, CVSS 5.3, published 16 Jul 2026) ## Vulnerabilities per week 3 vulnerabilities in the last four weeks, up from none in the four before. | Week of | Vulns | Critical | Exploited | | --- | --- | --- | --- | | 17 Aug 2026 | 1 | 0 | 0 | | 24 Aug 2026 | 0 | 0 | 0 | | 31 Aug 2026 | 0 | 0 | 0 | | 7 Sep 2026 | 0 | 0 | 0 | | 14 Sep 2026 | 0 | 0 | 0 | | 21 Sep 2026 | 0 | 0 | 0 | | 28 Sep 2026 | 0 | 0 | 0 | | 5 Oct 2026 | 0 | 0 | 0 | | 12 Oct 2026 | 0 | 0 | 0 | | 19 Oct 2026 | 0 | 0 | 0 | | 26 Oct 2026 | 1 | 0 | 0 | | 2 Nov 2026 | 2 | 0 | 0 | | 9 Nov 2026 | 0 | 0 | 0 | ## H2o technologies - [H2o Quicly](https://junglewise.ai/threats/technologies/quicly): 4 vulnerabilities ## Sources NVD, GitHub Security Advisories, OSV, the CISA Known Exploited Vulnerabilities catalog, FIRST EPSS and vendor advisories. Rebuilt every hour. Cite as: Junglewise Threat Intelligence, "H2o vulnerabilities", https://junglewise.ai/threats/vendors/h2o, 12 November 2026.