CVE-2026-40170

Name: CVE-2026-40170
Creator: NVD / NIST
Published: 2026-04-16T22:16:38.22+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 0.58%

Last modified Jun 17, 2026

CVE-2026-40170 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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. EPSS estimates a 0.58% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

7.5/10

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

EPSS Probability

0.58%

43.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-121

Affected Software

Vendor	Product	Versions
Tatsuhiro-T	Ngtcp2	< 1.22.1

References

https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5Patch
https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8fExploit, Mitigation, Patch, Vendor Advisory
http://www.openwall.com/lists/oss-security/2026/04/17/12Exploit, Mailing List, Mitigation, Patch, Third Party Advisory
https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8fExploit, Mitigation, Patch, Vendor Advisory

Timeline

Published: Apr 16, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-40170?

How severe is CVE-2026-40170?

CVE-2026-40170 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.58% probability of exploitation in the next 30 days.

How do I fix CVE-2026-40170?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-40170?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST