CVE-2026-40170 ngtcp2 has a qlog transport parameter serialization stack buffer overflow
A stack buffer overflow in ngtcp2 allows remote attackers to execute code or cause denial of service when qlog is enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40170?
CVE-2026-40170 is a high-severity memory corruption vulnerability in ngtcp2, published on 16 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
ngtcp2 is a C implementation of the IETF QUIC protocol. In versions prior to 1.22.1, ngtcp2_qlog_parameters_set_transport_params() serializes peer transport parameters into a fixed 1024-byte stack buffer without bounds checking. When qlog is enabled, a remote peer can send sufficiently large transport parameters during the QUIC handshake to cause writes beyond the buffer boundary, resulting in a stack buffer overflow. This affects deployments that enable the qlog callback and process untrusted peer transport parameters. This issue has been fixed in version 1.22.1. If developers are unable to immediately upgrade, they can disable the qlog on client.
Which versions are affected by CVE-2026-40170?
It affects 1 product.
Linux distribution packages (8)
ngtcp2 Red Hat:hummingbird:1 | All versions | 0:1.22.1-1.hum1 |
ngtcp2-crypto-gnutls Red Hat:hummingbird:1 | All versions | 0:1.22.1-1.hum1 |
ngtcp2-crypto-gnutls-devel Red Hat:hummingbird:1 | All versions | 0:1.22.1-1.hum1 |
ngtcp2-crypto-ossl Red Hat:hummingbird:1 | All versions | 0:1.22.1-1.hum1 |
ngtcp2-crypto-ossl-devel Red Hat:hummingbird:1 | All versions | 0:1.22.1-1.hum1 |
ngtcp2-devel Red Hat:hummingbird:1 | All versions | 0:1.22.1-1.hum1 |
ngtcp2-doc Red Hat:hummingbird:1 | All versions | 0:1.22.1-1.hum1 |
ngtcp2 openSUSE:Tumbleweed | All versions | 1.22.1-1.1 |
Products include Tatsuhiro-T Ngtcp2.
How do I fix CVE-2026-40170?
Upgrade to a fixed version.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-40170 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40170 exists.
Sources
Also known as ALPINE-CVE-2026-40170, DEBIAN-CVE-2026-40170, ECHO-c041-b4eb-d85f, GHSA-f523-465f-8c8f, RHSA-2026:9113, UBUNTU-CVE-2026-40170 and 1 more.