Is CVE-2026-40170 actively exploited?

No active exploitation of CVE-2026-40170 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2026-40170 be exploited remotely?

Yes. CVE-2026-40170 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-40170?

CVE-2026-40170 has a CVSS score of 7.5 (HIGH).

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HIGH

CVE-2026-40170

CWE-121Published: April 16, 2026· Updated: Apr 20, 2026

7.5

CVSS v3.1

EPSS:0.04%probability of exploitation in 30 daysPercentile:11.2th

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.

NVD Source

Technical Analysis

CVE-2026-40170 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.