Summary
AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing
Workarounds
Encode host names via the idna package prior to connecting.
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.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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The vulnerability will be patched in v4.14.2.
Frequently Asked Questions
- What is CVE-2026-63374? CVE-2026-63374 is a critical-severity security vulnerability in anyio (pip), affecting versions < 4.14.2. It is fixed in 4.14.2.
- Which versions of anyio are affected by CVE-2026-63374? anyio (pip) versions < 4.14.2 is affected.
- Is there a fix for CVE-2026-63374? Yes. CVE-2026-63374 is fixed in 4.14.2. Upgrade to this version or later.
- Is CVE-2026-63374 exploitable, and should I be worried? Whether CVE-2026-63374 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-63374 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-63374? Upgrade
anyioto 4.14.2 or later.