How severe is CVE-2026-63374?

No CVSS score has been assigned to CVE-2026-63374 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-63374?

CVE-2026-63374 affects the following packages: anyio (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-63374?

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.

How do I detect CVE-2026-63374 in my PyPI dependencies?

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.

How do I mitigate CVE-2026-63374 if there is no patch (or I can't update yet)?

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.

Is CVE-2026-63374 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-63374 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-63374?

CVE-2026-63374 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 21th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-63374?

CVE-2026-63374 is classified as CWE-295 (CWE-295), CWE-297 (CWE-297). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-63374 published, and has it been updated?

CVE-2026-63374 was published on September 22, 2026 and was last updated on October 29, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

CVE-2026-63374 — anyio

Fix: agronholm/anyio@68f5891

CVE-2026-63374 is a CWE-295 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

Also known asGHSA-82r6-8w77-94w6PYSEC-2026-4025

Published

Sep 22, 2026

Updated

Oct 29, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-63374.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs21th percentile — riskier than 21% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍anyio

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`anyio`	all versions	4.14.2`pip install --upgrade 'anyio==4.14.2'`

Detection & mitigation playbook

Open-source dependency

Detect
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.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This vulnerability is rated as having a Moderate severity for Red Hat products because exploitation requires an attacker to already be positioned to intercept network traffic, and the flaw only manifests when connecting to internationalized domain names containing non-ASCII characters. Within Red Hat supported…

Product	Fixed in	Advisory
Red Hat AI Inference Server 3.2	`rhaiis/vllm-cuda-rhel9:1790621718`	RHSA-2026:73929
Red Hat AI Inference Server 3.2	`rhaiis/vllm-rocm-rhel9:1790621713`	RHSA-2026:73930
Red Hat Ansible Automation Platform 2.6	`ansible-automation-platform-26/lightspeed-chatbot-rhel9:1791978798`	RHSA-2026:87120
Red Hat Ansible Automation Platform 2.7	`ansible-automation-platform-27/mcp-tools-rhel9:1790931895`	RHSA-2026:79378
Red Hat Ansible Automation Platform 2.7	`ansible-automation-platform-27/de-supported-rhel9:1792143400`	RHSA-2026:87124
Red Hat OpenShift AI 2.25	`rhoai/odh-ta-lmes-job-rhel9:1791553527`	RHSA-2026:87410
Red Hat OpenShift AI 3.4	`rhoai/odh-automl-rhel9:1791535789`	RHSA-2026:84734
Red Hat OpenShift AI 3.4	`rhoai/odh-mlserver-rhel9:1793110755`	RHSA-2026:92510

Frequently Asked Questions

### 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` p

O3 Security · Impact-Aware SCA

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