AnyIO CVE-2026-63374
CRITICAL
GHSA-82r6-8w77-94w6
Severity by source
AC:H because exploitation is gated on a divergent IDN plus a pre-existing hijack position and attacker-obtained certificate; successful MITM yields full C:H/I:H with no availability impact.
Lifecycle Timeline
4DescriptionCVE.org
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.
Articles & Coverage 1
AnalysisAI
Incorrect TLS hostname verification in the AnyIO Python library versions before 4.14.2 causes internationalized (non-ASCII) host names to be matched against the peer certificate using IDNA 2003 encoding from the standard library instead of IDNA 2008, so a host name like 'faß.de' is validated as 'fass.de' and an attacker holding a certificate for the wrong domain can pass certificate validation. This is not a remote unauthenticated code-execution bug: it is a certificate validation weakness (CWE-295) that only matters to applications using connect_tcp(tls=True) or TLSStream.wrap() with a divergent IDN host name and only when an attacker has already hijacked or redirected the connection at the network layer (DNS spoofing, BGP hijack, rogue access point) and can obtain a CA-issued certificate for the IDNA 2003 form of the name. …
Unlock full vulnerability intelligence
- Risk assessment & exploitation conditions
- Attack chain visualization
- Remediation with exact patch versions
- Threat intelligence from 22 sources
- Personal watchlist & email alerts
Free forever · No credit card required
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires ALL of: (1) the client application uses AnyIO connect_tcp(tls=True) or TLSStream.wrap() with a non-ASCII internationalized host name whose IDNA 2003 and IDNA 2008 ASCII encodings diverge (e.g. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | No CVSS vector was supplied by the vendor or NVD (CVSS N/A), so severity must be inferred from the description and patch. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade AnyIO to the vendor-released fix version 4.14.2 (PyPI package 'anyio'; release at https://github.com/agronholm/anyio/releases/tag/4.14.2), which applies IDNA 2008 encoding via the 'idna' package before host names are matched against the peer certificate. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, inventory all Python applications and services for AnyIO versions before 4.14.2, prioritizing externally exposed systems and those using connect_tcp(tls=True) or TLSStream.wrap() with internationalized hostnames; apply the vendor-released patch by upgrading to AnyIO 4.14.2 or later where feasible. …
Sign in for detailed remediation steps and compensating controls.
Threat intelligence, references, and detailed analysis are available after sign-in.
Wazuh SIEM platform versions 4.4.0 through 4.9.0 contain an unsafe deserialization vulnerability in the DistributedAPI t
BentoML version 1.4.2 and earlier contains an unauthenticated remote code execution vulnerability through insecure deser
pgAdmin 4 contains critical remote code execution vulnerabilities in the Query Tool download and Cloud Deployment endpoi
The renderLocalView function in render/views.py in graphite-web in Graphite 0.9.5 through 0.9.10 uses the pickle Python
BentoML is a Python library for building online serving systems optimized for AI apps and model inference. Rated critica
OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before 1.0.1h does not properly restrict processing of ChangeCiph
pyLoad download manager version prior to 0.5.0b3.dev77 exposes the Flask SECRET_KEY through an unauthenticated endpoint.
Langflow (a visual LLM pipeline builder) contains a critical unauthenticated code execution vulnerability (CVE-2026-3301
In Mercurial before 4.1.3, "hg serve --stdio" allows remote authenticated users to launch the Python debugger, and conse
Unauthenticated remote code execution affects Kestra OSS (the open-source event-driven orchestration platform) prior to
Unauthenticated remote code execution in Marimo ≤0.20.4 allows attackers to execute arbitrary system commands via the `/
pyLoad is the free and open-source Download Manager written in pure Python. Rated medium severity (CVSS 5.3), this vulne
Same weakness CWE-295 – Improper Certificate Validation
View allSame technique Information Disclosure
View allShare
External POC / Exploit Code
Leaving vuln.today