CVE-2026-63374 — anyio
Fix: agronholm/anyio#1208CVE-2026-63374 is a security vulnerability in anyio. A fix is available for anyio — see the affected versions and patch details below.
AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing
Real-World Exposure
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Description
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | anyio | all versions | 4.14.2pip install --upgrade 'anyio==4.14.2' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for anyio, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update anyio to 4.14.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-63374 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-63374 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-63374. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-63374 in your dependencies?
O3 Security finds CVE-2026-63374 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.