What is CVE-2026-44435?

CVE-2026-44435 is a high-severity vulnerability in H2o Quicly, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-07-16.

How severe is CVE-2026-44435?

High severity. CVSS v3 base score is 7.5 out of 10.

Resource exhaustion in H2o Quicly

CVE-2026-44435

Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 937d0e9, an assertion failure is raised when the total number of valid handshake messages received over a CRYPTO stream of a single packet number space exceeds 32KB, causing a Denial of Service. This issue has been fixed by commit 937d0e9.

Vulnerability class: DoS (Denial of Service)

EPSS: 0.005 (40.0th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

H2o Quicly — versions < 937d0e9

Weakness classification (CWE)

References

security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
security-advisories@github.com (Patch, x_refsource_MISC)

Frequently asked questions

What is CVE-2026-44435?: CVE-2026-44435 is a high-severity vulnerability in H2o Quicly, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-07-16.
How severe is CVE-2026-44435?: High severity. CVSS v3 base score is 7.5 out of 10.