EUVD-2026-83193
GHSA-5p39-cfhj-2xmp
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Trigger is the local process-pool worker boundary and requires the app to run worker code (PR:L/AV:L); impact is a pure availability deadlock with no confidentiality or integrity effect.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
4Blast Radius
ecosystem impact- 442 pypi packages depend on anyio (47 direct, 401 indirect)
Ecosystem-wide dependent count for version 4.14.2.
DescriptionCVE.org
AnyIO is a high level asynchronous concurrency and networking framework that works on top of either Trio or asyncio. Prior to 4.14.2, AnyIO starts process-pool workers with standard error connected to a pipe that the parent never drains, even though the documented behavior redirects all three standard streams. Worker code that writes enough attacker-influenced data to sys.stderr can fill the pipe and block before returning the standard-output protocol response, causing the awaiting process-pool call to remain blocked indefinitely. Applications that run untrusted or faulty worker code capable of producing substantial standard-error output are affected. This issue is fixed in version 4.14.2.
AnalysisAI
Denial of service in AnyIO versions prior to 4.14.2: the process-pool implementation behind to_process.run_sync() starts worker processes with stderr wired to a pipe that the parent never drains, so a worker that writes more than the roughly 64 KiB pipe buffer to sys.stderr blocks on write() before it can return its stdout protocol response, leaving the awaiting process-pool call hung indefinitely. Applications are exposed only if they actually use AnyIO's process pool and run worker functions whose stderr volume can be driven by untrusted or faulty input - for example verbose tracebacks or logging produced by attacker-influenced data - while code paths that never touch to_process, or that already close/redirect worker stderr, are unaffected. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Requires that the application uses AnyIO's process-pool API (to_process.run_sync) AND runs worker functions that write substantial data to sys.stderr - specifically enough to exceed the pipe buffer (~64KiB, per the fix's test). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor CVSS 4.0 vector (AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H, score 6.8) correctly frames this as a purely availability-impacting, locally-scoped flaw with no confidentiality or integrity effect - consistent with CWE-770 and the 'Denial Of Service' tag. … 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 to the vendor-released patch, AnyIO 4.14.2 or later (for example pip install "anyio>=4.14.2"), which fixes the flaw by adding sys.stderr = open(os.devnull, "w") inside process_worker() so worker stderr matches the documented redirection behavior; the change is tracked in PR https://github.com/agronholm/anyio/pull/1207, commit https://github.com/agronholm/anyio/commit/f1b7301c8264b0d2e8d24a5788fd29e93dea4040 and the 4.14.2 release, with advisory details at https://github.com/agronholm/anyio/security/advisories/GHSA-5p39-cfhj-2xmp. … Detailed patch versions, workarounds, and compensating controls in full report. |
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