CVE-2026-63374 — AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing
AnyIO is a high level asynchronous concurrency and networking framework that works on top of either Trio or asyncio. Prior to 4.14.2, connect_tcp() and TLSStream.wrap() can vali…
Published: 2026-09-22 · CVSS: 9.3 · CVSS 4.0
AnyIO is a high level asynchronous concurrency and networking framework that works on top of either Trio or asyncio. Prior to 4.14.2, connect_tcp() and TLSStream.wrap() can validate internationalized host names after the standard library converts them with IDNA 2003 instead of IDNA 2008. When a connection to a non-ASCII domain is hijacked or redirected, an attacker can obtain a legitimate certificate for the different ASCII hostname produced by IDNA 2003 and present it to the client, causing the malicious endpoint's certificate to validate. This issue is fixed in version 4.14.2.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7