CVE-2026-40170 — ngtcp2 has a qlog transport parameter serialization stack buffer overflow

Affected: ngtcp2, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat Hardened Images, Red Hat Enterprise Linux 8

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.

USN-8300-1 — ngtcp2 vulnerability

Affected: Ubuntu:Pro:22.04:LTS: ngtcp2, Ubuntu:24.04:LTS: ngtcp2, Ubuntu:25.10: ngtcp2, Ubuntu:26.04:LTS: ngtcp2

Zou Dikai discovered that ngtcp2 serialized peer transport parameters into a fixed 1024-byte stack buffer without bounds checking. When qlog was enabled, a remote attacker could possibly use this issue to execute arbitrary code.

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CVE-2026-40170 — ngtcp2 has a qlog transport parameter serialization stack buffer overflow

USN-8300-1 — ngtcp2 vulnerability