CVE-2016-4864: Dena h2o

High severity, CVSS 7.5. EPSS: 1.8% chance of exploitation in the next 30 days.

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.

Affected products

• Dena h2o: from 2.0.0, up to and including 2.0.3; version 2.1.0 only

Published 2017-05-12. Last modified 2026-06-17.