AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing
Impact
Services using internationalized (non-ASCII) domain names are potentially vulnerable to TLS connections made from AnyIO's connect_tcp() or directly via TLSStream.wrap() where the connection has (through other means) been hijacked and redirected to a malicious server. The attacker would obtain a legitimate certificate using the IDNA 2003 encoded version of the domain name and offer it to the connecting client, making the certificate validate properly on the client's end.
Patches
The vulnerability will be patched in v4.14.2.
Workarounds
Encode host names via the idna package prior to connecting.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | anyio | < 4.14.2 | 4.14.2 |
References
- https://github.com/agronholm/anyio/security/advisories/GHSA-82r6-8w77-94w6
- https://github.com/agronholm/anyio/pull/1208
- https://github.com/agronholm/anyio/commit/68f58915f82d9be8109ebbbd8f5d70577d43f2ce
- https://github.com/agronholm/anyio
- https://github.com/agronholm/anyio/releases/tag/4.14.2
- https://pypi.org/project/anyio
- https://github.com/advisories/GHSA-82r6-8w77-94w6
- https://nvd.nist.gov/vuln/detail/CVE-2026-63374
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-295, CWE-297- Platform
- Python (PyPI)
- Package
anyio- Disclosed
- 18.09.2026
- Updated
- 11.10.2026 15:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-4025 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-82r6-8w77-94w6 - CC BY 4.0
Vulnerability history: anyio
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 3
- First → latest
- 09.2026 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 1
- Medium 1
Disclosures per year
- 2026: 3
-
AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing this entry
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.