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Vulnerability · Published Oct 8, 2026 · Assigned by GitHub_M

CVE-2026-107286Pydantic AI: Concurrency-limited models can keep their slot when a streamed request ends early

High 7.5

In plain English

A high-severity security flaw in pydantic-ai from pydantic. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 39% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.4%top 60.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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 packages & fixed versions

EcosystemPackageFixed inAdvisory
PyPIpydantic-ai2.53.0GHSA-6fqq-452j-qhrp
PyPIpydantic-ai2.53.0PYSEC-2026-4276
PyPIpydantic-ai-slim2.53.0GHSA-6fqq-452j-qhrp
PyPIpydantic-ai-slim2.53.0PYSEC-2026-4285

Affected products (as reported)

VendorProductVersions
pydantic pydantic-ai >= 2.10.0, < 2.53.0
pydantic pydantic-ai-slim >= 2.10.0, < 2.53.0

Weakness: CWE-772 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References