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CVE-2026-40170

Tatsuhiro-t Ngtcp2 buffer overflow

7.5 HIGHPublic exploitEPSS 0.95%
  1. Published16 Apr 2026

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 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

Tatsuhiro-t Ngtcp2< 1.22.1

Remediation

Fixed in
Tatsuhiro-t Ngtcp2≥ 1.22.1

References

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Frequently asked

Is CVE-2026-40170 being actively exploited?

CVE-2026-40170 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.95%.

How severe is CVE-2026-40170?

CVE-2026-40170 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.95% probability of exploitation.

Which products are affected by CVE-2026-40170?

Affected products include Tatsuhiro-t Ngtcp2.

How do I fix CVE-2026-40170?

Upgrade affected software to a fixed version, for example Tatsuhiro-t Ngtcp2 1.22.1 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-40170 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.