CVE-2026-40170
ngtcp2 has a qlog transport parameter serialization stack buffer overflow
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.
INFO
Published Date :
April 16, 2026, 10:16 p.m.
Last Modified :
May 22, 2026, 2:26 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | MITRE-CVE |
Solution
- Update ngtcp2 to version 1.22.1.
- Disable qlog if unable to update immediately.
Public PoC/Exploit Available at Github
CVE-2026-40170 has a 3 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-40170.
| URL | Resource |
|---|---|
| https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5 | Patch |
| https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f | Exploit Mitigation Patch Vendor Advisory |
| http://www.openwall.com/lists/oss-security/2026/04/17/12 | Exploit Mailing List Mitigation Patch Third Party Advisory |
| https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f | Exploit Mitigation Patch Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-40170 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-40170
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
None
Python Dockerfile Jinja JavaScript HTML TypeScript CSS Shell
DSA and DLA for Debian last 14 days
Python
All Public RunWhen Helm Charts - Managed by terraform
Shell Dockerfile Go Template
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-40170 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-40170 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Reanalysis by [email protected]
May. 22, 2026
Action Type Old Value New Value Changed CPE Configuration OR *cpe:2.3:a:nghttp2:ngtcp2:*:*:*:*:*:*:*:* versions up to (excluding) 1.22.1 OR *cpe:2.3:a:tatsuhiro-t:ngtcp2:*:*:*:*:*:*:*:* versions up to (excluding) 1.22.1 -
Initial Analysis by [email protected]
May. 21, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:nghttp2:ngtcp2:*:*:*:*:*:*:*:* versions up to (excluding) 1.22.1 Added Reference Type GitHub, Inc.: https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f Types: Exploit, Mitigation, Patch, Vendor Advisory Added Reference Type CISA-ADP: https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f Types: Exploit, Mitigation, Patch, Vendor Advisory Added Reference Type CVE: http://www.openwall.com/lists/oss-security/2026/04/17/12 Types: Exploit, Mailing List, Mitigation, Patch, Third Party Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Apr. 20, 2026
Action Type Old Value New Value Added Reference https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f -
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Apr. 17, 2026
Action Type Old Value New Value Added Reference http://www.openwall.com/lists/oss-security/2026/04/17/12 -
New CVE Received by [email protected]
Apr. 16, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-121 Added Reference https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5 Added Reference https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f