How severe is CVE-2016-4864?

CVE-2016-4864 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2016-4864 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (76th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-4864?

CVE-2016-4864 primarily affects Dena H2o. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-4864?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2016-4864 published?

CVE-2016-4864 was published on 2017-05-12 and last updated on 2026-06-17.

CVE-2016-4864

CVE-2016-4864 is a high-severity vulnerability in Dena H2o with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-134.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 2% (76th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-134
Affected product: Dena H2o
Published: 2017-05-12
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is 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.
How severe is CVE-2016-4864?: CVE-2016-4864 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2016-4864 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (76th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-4864?: CVE-2016-4864 primarily affects Dena H2o. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2016-4864?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2016-4864 published?: CVE-2016-4864 was published on 2017-05-12 and last updated on 2026-06-17.

References

Affected products (3)

cpe:2.3:a:dena:h2o:*:*:*:*:*:*:*:*
cpe:2.3:a:dena:h2o:2.1.0:*:*:*:*:*:*:*
cpe:2.3:a:dena:h2o:2.1.0:beta1:*:*:*:*:*:*

More vulnerabilities in Dena H2o

CVE-2018-0608 — Critical (CVSS 9.8): Buffer overflow in H2O version 2.2.4 and earlier allows remote attackers to execute arbitrary code or cause a denial of…
CVE-2016-7835 — Critical (CVSS 9.1): Use-after-free vulnerability in H2O allows remote attackers to cause a denial-of-service (DoS) or obtain server…
CVE-2023-30847 — High (CVSS 8.2): H2O is an HTTP server. In versions 2.3.0-beta2 and prior, when the reverse proxy handler tries to processes a certain…
CVE-2023-44487 — High (CVSS 7.5): The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset…
CVE-2017-10908 — High (CVSS 7.5): H2O version 2.2.3 and earlier allows remote attackers to cause a denial of service in the server via specially crafted…
CVE-2017-10869 — High (CVSS 7.5): Buffer overflow in H2O version 2.2.2 and earlier allows remote attackers to cause a denial-of-service in the server via…

All CVEs affecting Dena H2o →

Other CWE-134 vulnerabilities

CVE-2012-1851 — Critical (CVSS 10.0): Format string vulnerability in the Print Spooler service in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2,…
CVE-2012-0242 — Critical (CVSS 10.0): Format string vulnerability in Advantech/BroadWin WebAccess before 7.0 allows remote attackers to execute arbitrary…
CVE-2011-2475 — Critical (CVSS 10.0): Format string vulnerability in ECTrace.dll in the iMailGateway service in the Internet Mail Gateway in OneBridge Server…
CVE-2011-1568 — Critical (CVSS 10.0): Format string vulnerability in the logText function in shmemmgr9.dll in IGSSdataServer.exe 9.00.00.11074, and…
CVE-2010-4235 — Critical (CVSS 10.0): Format string vulnerability in RealNetworks Helix Server 12.x, 13.x, and 14.x before 14.2, and Helix Mobile Server…
CVE-2011-0270 — Critical (CVSS 10.0): Format string vulnerability in nnmRptConfig.exe in HP OpenView Network Node Manager (OV NNM) 7.51 and 7.53 allows…

Browse all CWE-134 vulnerabilities →