CVE WatchJul 15, 2026

CVE-2026-40170

ngtcp2 is a C implementation of the IETF QUIC protocol. In versions prior to 1.22.1, ngtcp2_qlog_parameters_set_transport_params() serialize

CVSS

7.5

High

EPSS

0.8%

p52

KEV

—

Exploit Today

0-100

Published: Apr 16, 2026 · Last modified: Jul 15, 2026 · CWE-121 · CWE-120

EPSS · 30d

0.8%EPSS · 30 days0.8%

2026-06-302026-07-16

Technical 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.

Official references

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