Pydantic AI is a Python agent framework for building applications and workflows with Generative AI. From 2.10.0 until 2.53.0, streamed requests made through ConcurrencyLimitedModel or limit_model_concurrency can retain shared concurrency slots because anyio.CapacityLimiter associates an acquired slot with the borrowing task while streaming cleanup can run in a different task. Early stream termination, cancellation, consumer exceptions, or complete stream_text() consumption with debounce_by=0.1 can therefore leave capacity occupied, eventually preventing later requests that share the long-lived limiter from proceeding and causing a denial of service. Agent-level max_concurrency and non-streaming model requests are not affected. This issue is fixed in version 2.53.0.
Fix
Patch, vendor advisory and mitigation references on NVD 4
- https://github.com/pydantic/pydantic-ai/commit/453f19feeb7ab1d789f9393b1723c6a73b3d77b2 Patch
- https://github.com/pydantic/pydantic-ai/pull/9478 Patch, Vendor Advisory
- https://github.com/pydantic/pydantic-ai/releases/tag/v2.53.0 Patch, Release Notes, Vendor Advisory
- https://github.com/pydantic/pydantic-ai/security/advisories/GHSA-6fqq-452j-qhrp Mitigation, Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 7.5 · pydanticNVD modified 2026-10-13 14:36
Affected (CPE criteria) 1
cpe:2.3:a:pydantic:pydantic_ai:*:-:*:*:*:python:*:*
References 4
- https://github.com/pydantic/pydantic-ai/commit/453f19feeb7ab1d789f9393b1723c6a73b3d77b2 Patch
- https://github.com/pydantic/pydantic-ai/pull/9478 Patch, Vendor Advisory
- https://github.com/pydantic/pydantic-ai/releases/tag/v2.53.0 Patch, Release Notes, Vendor Advisory
- https://github.com/pydantic/pydantic-ai/security/advisories/GHSA-6fqq-452j-qhrp Mitigation, Vendor Advisory