CVE-2026-107286: Pydantic Pydantic-Ai

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

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.

Affected products

• Pydantic Pydantic-Ai: from 2.10.0, before 2.53.0 (fixed in 2.53.0)
• Pydantic Pydantic-Ai-Slim: from 2.10.0, before 2.53.0 (fixed in 2.53.0)

Published 2026-10-08. Last modified 2026-10-08.