CVE-2024-45397: h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3

Q: How do I fix CVE-2024-45397?

h2o: upgrade to 2024-10-10. Exact commands for each OS are on this page.

Q: Is CVE-2024-45397 being exploited?

CVE-2024-45397 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2024-45397 affect?

CVE-2024-45397 affects h2o. Severity is medium (CVSS 5.9). h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. When an HTTP request using TLS/1.3 early data on top of TCP Fast Open or QUIC 0-RTT packets is received and the IP-address-based access control is used, the access control

Q: How urgent is CVE-2024-45397?

Priority 35/100. Remotely exploitable, no login, no user action

Routine

MEDIUM 5.9REMOTEUPGRADE

CVE-2024-45397 is a medium-severity flaw (CVSS 5.9) affecting h2o. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. When an HTTP request using TLS/1.3 early data on top of TCP Fast Open or QUIC 0-RTT packets is received and the IP-address-based access control is used, the access control does not detect and prohibit HTTP requests conveyed by packets with a spoofed source address. This behavior allows attackers on the network to execute HTTP requests from addresses that are otherwise rejected by

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-284, CWE-290
Published	2024-10-11
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: dena

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

Am I affected?

Timeline

2024-10-11 15:15 UTCPublished CVE record published
2026-06-17 07:54 UTCUpdated Record last modified

dena h2o UPGRADE

Affected: < 2024-10-10

Fixed in: 2024-10-10

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 2024-10-10 (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.

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-2024-45397?

h2o: upgrade to 2024-10-10. Exact commands for each OS are on this page.

Is CVE-2024-45397 being exploited?

CVE-2024-45397 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-2024-45397 affect?

CVE-2024-45397 affects h2o. Severity is medium (CVSS 5.9). h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. When an HTTP request using TLS/1.3 early data on top of TCP Fast Open or QUIC 0-RTT packets is received and the IP-address-based access control is used, the access control

How urgent is CVE-2024-45397?

Priority 35/100. Remotely exploitable, no login, no user action

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References

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