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Vulnerability record · CVE-2026-40170 · published 16 April 2026

CVE-2026-40170: Tatsuhiro-t ngtcp2 stack-based buffer overflow vulnerability

TTatsuhiro T · Ngtcp2

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.

7.5 CVSS 3.1 High EPSS 0.96% · top 40.1% CWE-121 · Stack-based buffer overflowCWE-120 · Classic buffer overflow
7.5CVSS 3.1 base score
0.96%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
10References, 3 tagged exploit
15 Jul 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5 Patch
https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f ExploitMitigationPatchVendor Advisory
http://www.openwall.com/lists/oss-security/2026/04/17/12 ExploitMailing ListMitigationPatchThird Party Advisory
https://access.redhat.com/errata/RHSA-2026:22963
https://access.redhat.com/errata/RHSA-2026:25049
https://access.redhat.com/errata/RHSA-2026:9113
https://access.redhat.com/security/cve/CVE-2026-40170
https://bugzilla.redhat.com/show_bug.cgi?id=2459061
https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f ExploitMitigationPatchVendor Advisory
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40170.json

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Source: NIST National Vulnerability Database (record CVE-2026-40170), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.