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CVE-2026-63374— AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing

Quick assessment

Affected
agronholm anyio
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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 IDN

CVSS 9.3 · Critical

Affected Version Matrix 1

VendorProduct Version RangeStatus
agronholm anyio < 4.14.2 affected
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I. Basic Information for CVE-2026-63374

Vulnerability Information

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Vulnerability Title
AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing
Source: CVE Program / CVE List V5
Vulnerability Description
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 / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
证书验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
agronholm anyio < 4.14.2 -

II. Public POCs for CVE-2026-63374

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III. Intelligence Information for CVE-2026-63374

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Patches & Fixes for CVE-2026-63374 (2)

Other References for CVE-2026-63374 (2)

IV. Related Vulnerabilities

Same product: anyio
Same vendor: agronholm
Same weakness: CWE-295

V. Comments for CVE-2026-63374

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