CVE-2026-63349: Anyio AnyIO Run_process/open_process Ignores Extra_groups And Vulnerability

HIGH
Advisory Identifier: GHSA-3w57-8xmc-8v26
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CWE-266 CWE-269
Published
Advisory Summary

CVE-2026-63349 is a HIGH anyio run_process/open_process ignores extra_groups and vulnerability (CWE-266: Incorrect Privilege Assignment) affecting Anyio libraries in the PyPI ecosystem. The issue involves anyio run_process/open_process ignores extra_groups and can retain parent supplementary groups. Remediation is available by upgrading affected packages to version 4.14.2.

CVE-2026-63349 at a Glance

CVE Identifier CVE-2026-63349
GHSA Identifier GHSA-3w57-8xmc-8v26
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-266: Incorrect Privilege Assignment
Affected Product Anyio
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2026-63349

To remediate this vulnerability, upgrade all affected Anyio dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

anyio fixed: 4.14.2 
pip install anyio>=4.14.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show anyio

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-63349, inspect your installed packages using pip:

pip show anyio

Analyze the terminal output to locate any version of Anyio in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.14.2), your application is affected.

Note: The pip show anyio command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-266: Incorrect Privilege Assignment, where a product incorrectly assigns a privilege to a particular actor, creating an unintended sphere of control for that actor. In Anyio, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

AnyIO 4.14.0 accepts the POSIX extra_groups argument on anyio.run_process() and anyio.open_process(), but open_process() forwards the wrong variable to the backend: when extra_groups is not None, it assigns kwargs["extra_groups"] = group instead of extra_groups. As a result, callers cannot reliably clear or set supplementary groups for child processes. In a disposable Linux container, Python's subprocess.run(..., extra_groups=[]) clears a synthetic parent supplementary group list, while anyio.run_process(..., extra_groups=[]) preserves the parent groups. If group is also supplied, AnyIO passes an integer as extra_groups and the call fails with TypeError. This is a POSIX privilege-dropping correctness issue for applications that rely on AnyIO subprocess helpers to launch less-privileged child processes.

CVE-2026-63349 Affected Anyio Versions

1 component(s)
Fixed Versions:
4.14.2
Product / Package Ecosystem Affected Versions Fixed Version
anyio
pypi/anyio
PyPI
≥ 4.14.0
< 4.14.2
4.14.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/agronholm/anyio/security/advisories/GHSA-3w57-8xmc-8v26
Anyio Source Repository REPOSITORY
https://github.com/agronholm/anyio/pull/1209
Security Fix Commit FIX COMMIT
https://github.com/agronholm/anyio/commit/eb562e6462ee46b1904e50b02ce00a858cdeb200
Anyio Source Repository REPOSITORY
https://github.com/agronholm/anyio
Anyio Release RELEASE
https://github.com/agronholm/anyio/releases/tag/4.14.2

Frequently Asked Questions

What is CVE-2026-63349?
CVE-2026-63349 is a security vulnerability in Anyio involving AnyIO run_process/open_process ignores extra_groups and can retain parent supplementary groups under CWE-266: Incorrect Privilege Assignment.
Which Anyio versions are affected?
Affected versions include releases prior to 4.14.2 across affected packages: anyio.
What version fixes CVE-2026-63349?
Upgrading to 4.14.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is anyio affected?
Yes, anyio is affected in releases prior to 4.14.2. Upgrade your dependency to 4.14.2 or later.
What CWE is associated with CVE-2026-63349?
CVE-2026-63349 is classified under CWE-266: Incorrect Privilege Assignment (A product incorrectly assigns a privilege to a particular actor, creating an unintended sphere of control for that actor.).
How can I check PyPI dependencies for CVE-2026-63349?
Run the dependency tree command: 'pip show anyio'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3w57-8xmc-8v26",
  "modified" : "2026-09-18T17:17:23Z",
  "published" : "2026-09-18T17:17:23Z",
  "aliases" : [ "CVE-2026-63349" ],
  "summary" : "AnyIO run_process/open_process ignores extra_groups and can retain parent supplementary groups",
  "details" : "AnyIO 4.14.0 accepts the POSIX extra_groups argument on anyio.run_process() and anyio.open_process(), but open_process() forwards the wrong variable to the backend: when extra_groups is not None, it assigns kwargs[\"extra_groups\"] = group instead of extra_groups. As a result, callers cannot reliably clear or set supplementary groups for child processes. In a disposable Linux container, Python's subprocess.run(..., extra_groups=[]) clears a synthetic parent supplementary group list, while anyio.run_process(..., extra_groups=[]) preserves the parent groups. If group is also supplied, AnyIO passes an integer as extra_groups and the call fails with TypeError. This is a POSIX privilege-dropping correctness issue for applications that rely on AnyIO subprocess helpers to launch less-privileged child processes.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "anyio"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.14.0"
      }, {
        "fixed" : "4.14.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/agronholm/anyio/security/advisories/GHSA-3w57-8xmc-8v26"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/agronholm/anyio/pull/1209"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/agronholm/anyio/commit/eb562e6462ee46b1904e50b02ce00a858cdeb200"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/agronholm/anyio"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/agronholm/anyio/releases/tag/4.14.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-266", "CWE-269" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-18T17:17:23Z",
    "nvd_published_at" : null
  }
}