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CVE-2026-40170— ngtcp2 has a qlog transport parameter serialization stack buffer overflow

Quick assessment

Affected
ngtcp2 ngtcp2
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

ngtcp2是ngtcp2开源的一个库。 ngtcp2 1.22.1之前版本存在安全漏洞，该漏洞源于启用qlog时，ngtcp2_qlog_parameters_set_transport_params函数将传输参数序列化到固定大小的栈缓冲区时未进行边界检查，可能导致栈缓冲区溢出。

CVSS 7.5 · High EPSS 0.78% · P56

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
ngtcp2 ngtcp2 < 1.22.1 affected
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I. Basic Information for CVE-2026-40170

Vulnerability Information
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Vulnerability Title
ngtcp2 has a qlog transport parameter serialization stack buffer overflow
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
栈缓冲区溢出
Source: CVE Program / CVE List V5
Vulnerability Title
ngtcp2 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
ngtcp2是ngtcp2开源的一个库。 ngtcp2 1.22.1之前版本存在安全漏洞，该漏洞源于启用qlog时，ngtcp2_qlog_parameters_set_transport_params函数将传输参数序列化到固定大小的栈缓冲区时未进行边界检查，可能导致栈缓冲区溢出。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
ngtcp2 ngtcp2 < 1.22.1 -

II. Public POCs for CVE-2026-40170

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III. Intelligence Information for CVE-2026-40170

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Vendor Advisories for CVE-2026-40170 (1)

IV. Related Vulnerabilities

Same product: ngtcp2
Same vendor: ngtcp2
Same weakness: CWE-121