PT-2026-60592 · H2O · Quicly

CVE-2026-44433 · Published 2026-07-16 · Updated 2026-07-16

Mitre

CVSS v3.1

5.3

Medium

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 8b178e6, an adversarial peer could send a STREAM frame carrying just one byte at the largest offset being permitted to obtain additional flow control credit, which under certain circumstances could lead to a Denial of Service. Assuming the application prepares a receive buffer for storing all data that arrive out-of-order, up to the largest offset being received, this behavior could lead to the application allocating large amount of memory with the peer sending only a handful of packets, resulting in memory exhaustion. In addition to the receive buffer allocation strategy, the severity of this vulnerability depends on how the application controls the stream concurrency. In case of the H2O HTTP server, under its default setting, this bug increases the maximum amount of memory allocated per connection by about 4 times. This issue has been fixed by commit 8b178e6.

Fix

Allocation of Resources Without Limits

Resource Exhaustion

Weakness Enumeration

CWE-770

CWE-400

Related Identifiers

CVE-2026-44433

Affected Products

Quicly

References · 3

• https://nvd.nist.gov/vuln/detail/CVE-2026-44433 · Security Note
• https://github.com/h2o/quicly/commit/8b178e692c51a3b1031612ef89f03a53aac63c15 · Note
• https://github.com/h2o/quicly/security/advisories/GHSA-f7qr-4p37-9gx9 · Note