H2O versions 2.0.3 and earlier and 2.1.0-beta2 and earlier allows remote attackers to…
Priority LOW 36CWE-134Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- No fix listed
Attack profile from CVSS 3.0 · NVD. Fix status from CNA. Impact type from CWE-134 and the CVSS impact.
Summary
H2O versions 2.0.3 and earlier and 2.1.0-beta2 and earlier allows remote attackers to cause a denial-of-service (DoS) via format string specifiers in a template file via fastcgi, mruby, proxy, redirect or reproxy.
Why it matters now
EPSS 0.01802 78th percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Kazuho Oku | H2O | up to 2.0.3; up to 2.1.0-beta2 | — | No fix listed | CNA |
- H2O VendorKazuho Oku Affected up to 2.0.3; up to 2.1.0-beta2 Fixed in — No fix listed CNA
CPE configurations NVD · 3
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:dena:h2o:*:*:*:*:*:*:*:* | 2.0.0 – 2.0.3 | Vulnerable | Kazuho Oku |
| cpe:2.3:a:dena:h2o:2.1.0:*:*:*:*:*:*:* | 2.1.0 | Vulnerable | Kazuho Oku |
| cpe:2.3:a:dena:h2o:2.1.0:beta1:*:*:*:*:*:* | 2.1.0 beta1 | Vulnerable | Kazuho Oku |
- cpe:2.3:a:dena:h2o:*:*:*:*:*:*:*:* Versions 2.0.0 – 2.0.3 Vulnerable ·Kazuho Oku
- cpe:2.3:a:dena:h2o:2.1.0:*:*:*:*:*:*:* Versions 2.1.0 Vulnerable ·Kazuho Oku
- cpe:2.3:a:dena:h2o:2.1.0:beta1:*:*:*:*:*:* Versions 2.1.0 beta1 Vulnerable ·Kazuho Oku
Remediation
No fixed version listed by the sources yet.
Timeline
- 2026-10-02 Threatist record created from CVE-2016-4864
- 2026-10-03 Alias added: GHSA-h4xp-827w-ffh7
References
Advisory 1
More Kazuho Oku H2o vulnerabilities
- TI-2023-23979 The HTTP/2 protocol allows a denial of service (server resource consumption) because… KEVCVSS 3.1HIGH 7.5
- TI-2018-00565 Memory corruption in Kazuho Oku H2O CVSS 3.0CRITICAL 9.8
- TI-2016-06584 Use after free in Kazuho Oku H2O CVSS 3.0CRITICAL 9.1
- TI-2023-14626 H2O vulnerable to read from uninitialized pointer in the reverse proxy handler CVSS 3.1HIGH 8.2
- TI-2016-04162 lib/http2/connection.c in H2O before 1.7.3 and 2.x before 2.0.0-beta5 mishandles HTTP/2… CVSS 3.0HIGH 7.5
- TI-2017-07997 Improper input validation in Kazuho Oku H2O CVSS 3.0HIGH 7.5
Sources
- CVE-2016-4864 · CVE Program
- CVE-2016-4864 · NVD
- FIRST EPSS
- GHSA-h4xp-827w-ffh7 · GitHub Advisory Database · CC BY 4.0
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