Answer in brief
CVE-2026-63374 records a Critical severity vulnerability in AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing. The current sources do not mark it as known exploited. The current feed maps anyio (pip), anyio (pypi). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps anyio (pip), anyio (pypi). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| anyiopip | <4.14.2 | 4.14.2 |
| anyiopypi | >=0 <4.14.2 | 4.14.2 |
Published upstream
Sep 18, 2026
Evidence: source:ghsa:source_dates:source-dates:recordSource modified
Sep 18, 2026
Evidence: source:ghsa:source_dates:source-dates:recordFirst seen by HOL
Sep 18, 2026
### 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.
Quoted source text, attributed separately from HOL analysis.