CVE-2026-40170
HighCVSS 7.5Exploitation Probability (EPSS)
Elevated risk52th percentile - higher than 52% of all known CVEs
Summary
A stack buffer overflow vulnerability exists in ngtcp2, a C implementation of the IETF QUIC protocol. The function ngtcp2_qlog_parameters_set_transport_params() copies peer transport parameters into a fixed 1024-byte stack buffer without bounds checking, allowing a remote attacker to write beyond the buffer during the QUIC handshake when qlog logging is enabled.
Risk Assessment
Organizations are at risk of remote code execution or denial of service (DoS) via crafted QUIC transport parameters. This affects deployments with qlog enabled that process untrusted transport parameters.
Recommendation
Upgrade ngtcp2 to version 1.22.1 or later immediately. If an upgrade is not possible, disable the qlog feature on the client.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

