H2O use of externally-controlled format string


H2O is an open source web server software. H2O uses externally-controlled format strings (CWE-134) in the code which output error logs.

Kazuho Oku reported this vulnerability to IPA to notify users of its solution through JVN. JPCERT/CC and Kazuho Oku coordinated under the Information Security Early Warning Partnership.
CVSS Severity (What is CVSS?)

CVSS V3 Severity:
Base Metrics 3.7 (Low) [IPA Score]
  • Attack Vector: Network
  • Attack Complexity: High
  • Privileges Required: None
  • User Interaction: None
  • Scope: Unchanged
  • Confidentiality Impact: None
  • Integrity Impact: None
  • Availability Impact: Low
CVSS V2 Severity:
Base Metrics 4.3 (Medium) [IPA Score]
  • Access Vector: Network
  • Access Complexity: Medium
  • Authentication: None
  • Confidentiality Impact: None
  • Integrity Impact: None
  • Availability Impact: Partial
Affected Products

Kazuho Oku
  • H2O version 2.0.3 and earlier
  • H2O version 2.1.0-beta2 and earlier


An unauthenticated remote attacker may cause a denial-of-service (DoS) condition.

[Update the Software]
Update to the latest version according to the information provided by the developer.
Vendor Information

Kazuho Oku
CWE (What is CWE?)

  1. Uncontrolled Format String(CWE-134) [IPA Evaluation]
CVE (What is CVE?)

  1. CVE-2016-4864

  1. JVN : JVN#94779084
  2. National Vulnerability Database (NVD) : CVE-2016-4864
Revision History

  • [2016/09/15]
      Web page was published
      References : Content was added