CVE-2016-4864

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.

Published: 2017-05-12 Last update: 2026-05-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2016-4864 is rated Moderate Risk (56.7/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.80%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2016-4864

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 1.60% 1.80% +0.20%
2 2025-03-30 2.21% 1.60% -0.61%
3 2025-03-29 — 2.21% —

Full EPSS history (6 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2016-4864

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.0 HIGH
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2016-4864

OS Trackers for CVE-2016-4864

vendor priority summary link
debian unimportant CVE-2016-4864 unimportant priority: Debian including 1 source packages (h2o), 2 status rows across 2 suites (bookworm, bullseye): resolved 2. https://security-tracker.debian.org/tracker/CVE-2016-4864

Affected software / configurations for CVE-2016-4864

Vendor Product Version Raw CPE
dena h2o >= 2.0.0, <= 2.0.3 cpe:2.3:a:dena:h2o:*:*:*:*:*:*:*:*
dena h2o 2.1.0 cpe:2.3:a:dena:h2o:2.1.0:*:*:*:*:*:*:*
dena h2o 2.1.0 cpe:2.3:a:dena:h2o:2.1.0:beta1:*:*:*:*:*:*

References for CVE-2016-4864

URL Tags
https://github.com/h2o/h2o/issues/1077 Patch Third Party Advisory
https://jvn.jp/en/jp/JVN94779084/index.html Third Party Advisory VDB Entry
cvelogic Threat Intelligence