What’s Vulnerable › Vulnerabilities

CVE-2024-45397: H2O alllows bypassing address-based access control with 0-RTT

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-10-11 · updated 2026-06-17
• Weakness: CWE-284

Description

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 the address-based access control. The vulnerability has been addressed in commit 15ed15a. Users may disable the use of TCP FastOpen and QUIC to mitigate the issue.

Affected products

• h2o: before 2024-10-10 — fixed in 2024-10-10

How to fix

Upgrade to a fixed version: h2o 2024-10-10. Check the vendor advisory for mitigations.

References

• https://github.com/h2o/h2o/commit/15ed15a2efb83a77bb4baaa5a119e639c2f6898a
• https://github.com/h2o/h2o/security/advisories/GHSA-jf2c-xjcp-wg4c
• https://h2o.examp1e.net/configure/http3_directives.html

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