CVE-2026-63374Network attack vectorHinoki check available

Domain impersonation via IDNA 2003 hostname conversion

Published Sep 22, 2026 · Updated Sep 22, 2026

Improper TLS hostname validation in AnyIO before 4.14.2 allows remote attackers to impersonate internationalized domains after traffic redirection. TLSStream.wrap passes a Unicode hostname to the standard library, which converts it with IDNA 2003 and validates the peer certificate against the resulting, potentially different ASCII name. Exploitation requires a non-ASCII destination, connection redirection, and a legitimate certificate for the IDNA 2003 name; success exposes or alters TLS-protected data.

CVSS severity9.3
Critical
EPSS probability0.29%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Get started

Summary

What happened

Improper TLS hostname validation in AnyIO before 4.14.2 allows remote attackers to impersonate internationalized domains after traffic redirection. TLSStream.wrap passes a Unicode hostname to the standard library, which converts it with IDNA 2003 and validates the peer certificate against the resulting, potentially different ASCII name. Exploitation requires a non-ASCII destination, connection redirection, and a legitimate certificate for the IDNA 2003 name; success exposes or alters TLS-protected data.

The record

CVE
CVE-2026-63374
Published
Sep 22, 2026
Updated
Sep 22, 2026
Vendor
Alex Grönholm
Product
AnyIO
Classifications
CWE-295, CWE-297, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=< 4.14.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Alex Grönholm · AnyIOversion=< 4.14.2

Published CVSS scores

9.3GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

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.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-295Improper Certificate Validation
CWE-297Improper Validation of Certificate with Host Mismatch
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Get started to see how Hinoki identifies affected software and validates exploitability in your environment.

Get started