CVE-2026-40170Public exploitNetwork attack vector

Service interruption via qlog stack buffer overflow

Published Apr 16, 2026 · Updated Apr 16, 2026

Stack buffer overflow in ngtcp2 before 1.22.1 allows remote attackers to interrupt QUIC services through crafted transport parameters. ngtcp2_qlog_parameters_set_transport_params() appends peer-controlled fields and hex data to a 1024-byte stack buffer without an end-to-end size guard. Normal handshake processing reaches the path without authentication only when the qlog callback is enabled, and the documented impact is limited to availability.

CVSS severity7.5
High
EPSS probability0.78%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack buffer overflow in ngtcp2 before 1.22.1 allows remote attackers to interrupt QUIC services through crafted transport parameters. ngtcp2_qlog_parameters_set_transport_params() appends peer-controlled fields and hex data to a 1024-byte stack buffer without an end-to-end size guard. Normal handshake processing reaches the path without authentication only when the qlog callback is enabled, and the documented impact is limited to availability.

The record

CVE
CVE-2026-40170
Published
Apr 16, 2026
Updated
Apr 16, 2026
Vendor
ngtcp2
Product
ngtcp2
Classifications
CWE-121, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 16, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 16, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.22.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ngtcp2 · ngtcp2version=< 1.22.1

Published CVSS scores

7.5GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-121Stack-based Buffer Overflow
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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