{"id":"GHSA-5p39-cfhj-2xmp","summary":"AnyIO process-pool workers can block indefinitely on undrained stderr","details":"### Impact\nAnyIO starts process-pool workers with stderr connected to a pipe but never drains that pipe. The worker redirects stdin and stdout to /dev/null to protect its protocol, but does not redirect stderr even though the documentation says all three standard streams are redirected. Worker code that writes enough attacker-influenced data to stderr can fill the pipe, block before returning the stdout protocol response, and wedge the awaiting process-pool call.\n\nAnyone who runs untrusted or faulty code that writes too much to `stderr` is at risk.\n\n### Patches\nThis vulnerability will be patched in v4.14.2.\n\n### Workarounds\nClosing `sys.stderr` in the target function should at least prevent the deadlock.","aliases":["CVE-2026-64847"],"modified":"2026-09-18T17:30:10.151287447Z","published":"2026-09-18T17:17:10Z","database_specific":{"github_reviewed_at":"2026-09-18T17:17:10Z","nvd_published_at":null,"cwe_ids":["CWE-770"],"severity":"MODERATE","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/agronholm/anyio/security/advisories/GHSA-5p39-cfhj-2xmp"},{"type":"WEB","url":"https://github.com/agronholm/anyio/pull/1207"},{"type":"WEB","url":"https://github.com/agronholm/anyio/commit/f1b7301c8264b0d2e8d24a5788fd29e93dea4040"},{"type":"PACKAGE","url":"https://github.com/agronholm/anyio"},{"type":"WEB","url":"https://github.com/agronholm/anyio/releases/tag/4.14.2"}],"affected":[{"package":{"name":"anyio","ecosystem":"PyPI","purl":"pkg:pypi/anyio"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.14.2"}]}],"versions":["1.0.0","1.0.0a1","1.0.0a2","1.0.0b1","1.0.0b2","1.0.0rc1","1.0.0rc2","1.1.0","1.2.0","1.2.1","1.2.2","1.2.3","1.3.0","1.3.1","1.4.0","2.0.0","2.0.0b1","2.0.0b2","2.0.0rc1","2.0.0rc2","2.0.1","2.0.2","2.1.0","2.2.0","3.0.0","3.0.0rc1","3.0.0rc2","3.0.0rc3","3.0.0rc4","3.0.1","3.1.0","3.2.0","3.2.1","3.3.0","3.3.1","3.3.2","3.3.3","3.3.4","3.4.0","3.5.0","3.6.0","3.6.1","3.6.2","3.7.0","3.7.0rc1","3.7.1","4.0.0","4.0.0rc1","4.1.0","4.10.0","4.11.0","4.12.0","4.12.1","4.13.0","4.14.0","4.14.1","4.2.0","4.3.0","4.4.0","4.5.0","4.5.1","4.5.2","4.6.0","4.6.1","4.6.2","4.6.2.post1","4.7.0","4.8.0","4.9.0"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-5p39-cfhj-2xmp/GHSA-5p39-cfhj-2xmp.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"}]}