What is CVE-2026-44436?

CVE-2026-44436 is a high-severity vulnerability in H2o Quicly, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 7.5/10. Published 2026-07-16.

How severe is CVE-2026-44436?

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

Buffer overflow in H2o Quicly

CVE-2026-44436

Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 8b178e6, Quicly is vulnerable to a Denial of Service attack through connection state corruption. In QUIC Invariants, the…

Vulnerability class: Buffer Overflow

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 < 8b178e6

Weakness classification (CWE)

CWE-120 — Buffer Copy without Checking Size of Input (Classic Buffer Overflow)
CWE-787 — Out-of-bounds Write

References

security-advisories@github.com (x_refsource_CONFIRM)
security-advisories@github.com (x_refsource_MISC)

Frequently asked questions

What is CVE-2026-44436?: CVE-2026-44436 is a high-severity vulnerability in H2o Quicly, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 7.5/10. Published 2026-07-16.
How severe is CVE-2026-44436?: High severity. CVSS v3 base score is 7.5 out of 10.