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Vulnerabilities

Vulnerability · CVE-2026-40170

ngtcp2 is a C implementation of the IETF QUIC protocol.

Published Apr 16, 2026 · catalog updated Jul 15, 2026 · ngtcp2 is a C

Check if you run it

No confirmed exploitation is on record for CVE-2026-40170. EPSS is 0.95%. Act only if a listed version of ngtcp2 is a C is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (ngtcp2 is a C).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.95%
Remediation
Advisory link
Affected products
cpe tatsuhiro-t/ngtcp2

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe tatsuhiro-t/ngtcp2version unspecified

How to fix CVE-2026-40170

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-40170. EPSS is 0.95%. Act only if a listed version of ngtcp2 is a C is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-120: Classic Buffer Overflow; CWE-121: Stack-based Buffer Overflow. EPSS 0.95%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Apr 16, 2026 · NIST NVD

    Detected

    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 s

  2. Jul 15, 2026 · NIST NVD

    Updated

    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 s

Sources

  • CVE.orgVulnerability recordCVE-2026-40170

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-40170

    30-day exploitation probability 1.0%

    first.org
  • NIST NVDVulnerability recordCVE-2026-40170

    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 suffic

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.