CVE-2016-7835: Use-after-free vulnerability in H2O allows remote attackers to cause a denial-of-service (DoS) or obtain serve

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CRITICAL 9.1REMOTEUPGRADEDOWNGRADE

CVE-2016-7835 is a critical-severity flaw (CVSS 9.1) affecting h2o, h2o. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Use-after-free vulnerability in H2O allows remote attackers to cause a denial-of-service (DoS) or obtain server certificate private keys and possibly other information.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.2% (top 17%)
CISA exploited list	No
Weakness	CWE-416
Published	2017-06-09
Last modified	2026-06-17

Publisher (CNA): JPCERT/CC · Vendor: dena · h2o project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2017-06-09 16:29 UTCPublished CVE record published
2026-06-17 00:53 UTCUpdated Record last modified

dena h2o UPGRADE

Affected: <= 2.0.4

Fixed in: newer than 2.0.4

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy h2o || rpm -q h2o || h2o --version

2. UPGRADE to newer than 2.0.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade h2o

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade h2o

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

h2o project h2o DOWNGRADE

Affected: 2.1.0 beta3

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.1.0

1. Check installed version

apt-cache policy h2o || rpm -q h2o || h2o --version

2. No fixed release: DOWNGRADE to a release before 2.1.0 (Debian / Ubuntu)

apt-cache madison h2o sudo apt install h2o=<VERSION_BEFORE_2.1.0> sudo apt-mark hold h2o

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list h2o sudo dnf downgrade h2o-<VERSION_BEFORE_2.1.0> sudo dnf versionlock add h2o

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2016-7835?

h2o: upgrade to newer than 2.0.4; h2o: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2016-7835 being exploited?

CVE-2016-7835 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2016-7835 affect?

CVE-2016-7835 affects h2o, h2o. Severity is critical (CVSS 9.1). Use-after-free vulnerability in H2O allows remote attackers to cause a denial-of-service (DoS) or obtain server certificate private keys and possibly other information.

How urgent is CVE-2016-7835?

Priority 58/100. Critical severity; Remotely exploitable, no login, no user action

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References

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