CVE-2026-40170CWE-121

ngtcp2 has a qlog transport parameter serialization stack buffer overflow

High · published April 16, 2026

CVSS v3.1
7.5
EPSS
1%
Percentile
61.1
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
7.5 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v4.0
Not supplied
EPSS
0.00955 · 61.1th percentile
Weakness
CWE-121 · Stack-based Buffer Overflow
Published
2026-04-16T21:34Z
EPSS history
Timeline
  • 16 APR 21:34Z
    ngtcp2 has a qlog transport parameter serialization stack buffer overflow
    cvelistv5