Improper Validation of Certificate with Host Mismatch Affecting anyio package, versions [,4.14.2)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
Do your applications use this vulnerable package?
In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.
Test your applications- Snyk IDSNYK-PYTHON-ANYIO-19958324
- published20 Sept 2026
- disclosed18 Sept 2026
- creditUnknown
Introduced: 18 Sep 2026
NewCVE-2026-63374 (opens in a new tab)How to fix?
Upgrade anyio to version 4.14.2 or higher.
Overview
anyio is a High level compatibility layer for multiple asynchronous event loop implementations
Affected versions of this package are vulnerable to Improper Validation of Certificate with Host Mismatch via TLSStream.wrap() in src/anyio/streams/tls.py, which resolves international domain names using IDNA 2003 instead of IDNA 2008 when constructing the server_hostname passed to wrap_bio(). Because IDNA 2003 and IDNA 2008 can map the same Unicode label to different ASCII representations, a TLS connection to an internationalized domain name may be established against a certificate whose Subject Alternative Name was encoded under IDNA 2008, causing the hostname verification to succeed against a certificate that does not legitimately cover the intended host. An attacker positioned to present such a certificate can perform a MitM attack against clients connecting to internationalized hostnames.