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CVE-2026-40170

ngtcp2 has a qlog transport parameter serialization stack buffer overflow

Published: Apr 16, 2026Updated: May 21, 2026 Sources: CVE List NVDCWE-121
NVD MITRE
7.5CVSSHIGH
EPSS Score
0.6%
Top 57.0%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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 Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:NA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:NIntegrity
None
A:HAvailability
High
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Weaknesses

CWE-121

Affected Products

ngtcp2ngtcp2
Library
OSS Libraries / generic-library
ngtcp2nghttp2
Library
OSS Libraries / generic-library
ngtcp2oss-projectOSS Libraries
nghttp2oss-projectOSS Librariesaka nghttp2, ngtcp2

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available

MITRE ATT&CK

1 technique
Privilege Escalation
View detailed technique mapping

References

https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f
github.com
https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5
github.com
http://www.openwall.com/lists/oss-security/2026/04/17/12
openwall.com

Timeline

Published
Apr 16, 2026
Last Updated
May 21, 2026

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