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High, CVSS 7.5amended

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

CVE-2026-107286GHSA-6fqq-452j-qhrp

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (pydantic-ai 2.53.0; pydantic-ai-slim 2.53.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-107286: 0.45% estimated exploitation activity in the next 30 days; percentile 39.13 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

This issue was posted by Codex Desktop using gpt-6.1-sol on behalf of David. Summary Applications that wrap a model with ConcurrencyLimitedModel or limitmodelconcurrency can permanently lose shared concurrency capacity when a streamed request releases its slot from a different task than the one that acquired it. This can happen when a stream ends early, and also when a stream is fully consumed using the default streamtext() debouncing. In an application that exposes an affected streaming endpoint to network clients and shares a long-lived model limiter across requests, a client can repeatedly start a stream and disconnect. The completed requests retain their slots, eventually preventing subsequent requests that share the limiter from proceeding. Agent-level maxconcurrency and non-streaming model requests are not affected by this defect. Details The built-in limiter uses anyio.CapacityLimiter, which associates each acquired slot with its borrowing task. Pydantic AI's streaming…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-6fqq-452j-qhrp

  2. Revision 2 · amended ·

    Amended from osv record GHSA-6fqq-452j-qhrp

  3. Revision 1 · created ·

    Published from ghsa record GHSA-6fqq-452j-qhrp

Agent brief

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# Patch Next advisory brief: CVE-2026-107286

Advisory: Pydantic AI: Concurrency-limited models can keep their slot when a streamed request ends early
IDs: CVE-2026-107286, GHSA-6fqq-452j-qhrp
Record: https://patchnext.com/advisories/cve-2026-107286 (revision 3, source checked 26 Oct 2026, 13:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pydantic-ai 2.53.0; pydantic-ai-slim 2.53.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pydantic-ai: affected >= 2.10.0, < 2.53.0; fixed in 2.53.0
- PyPI pydantic-ai-slim: affected >= 2.10.0, < 2.53.0; fixed in 2.53.0

## Suggested inspection (read-only)
- `python -m pip show pydantic-ai`: prints the installed version. Run with the environment that serves production active.
- `python -m pip show pydantic-ai-slim`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pydantic-ai, pydantic-ai-slim.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6fqq-452j-qhrp (GitHub-reviewed advisory GHSA-6fqq-452j-qhrp lists affected ranges: PyPI pydantic-ai >=2.10.0 =2.10.0 <2.53.0)
- Verified: https://osv.dev/vulnerability/GHSA-6fqq-452j-qhrp (OSV record GHSA-6fqq-452j-qhrp lists affected ranges: PyPI pydantic-ai >=2.10.0 =2.10.0 <2.53.0 (fixed))

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