CVE-2026-40170

HIGH 7.5

ngtcp2 has a qlog transport parameter serialization stack buffer overflow

CVSS Score

7.5

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-121
Vendor	ngtcp2
Product	ngtcp2
Published	Apr 16, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Affected Versions

ngtcp2 / ngtcp2

< 1.22.1

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f github.com: https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5