What’s Vulnerable › Vulnerabilities

CVE-2026-107290: Pydantic AI: Event loop blocked by quadratic title extraction in `web_fetch`

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-10-08 · updated 2026-10-13
• Weakness: CWE-1333

Description

Pydantic AI is a Python agent framework for building applications and workflows with Generative AI. From 1.77.0 until 1.107.6 and 2.44.0, the local web_fetch_tool and the WebFetch local fallback process server-controlled responses with quadratic title extraction, whitespace normalization, and ordered-list numbering. An attacker-controlled page of modest size can therefore block the event loop for an extended period, stalling other agent runs and requests, while unsupported codecs or excessive HTML or JSON nesting can abort an individual run. This issue is fixed in versions 1.107.6 and 2.44.0.

Affected products

• pydantic-ai: from 1.77.0 before 1.107.6; from 2.0.0 before 2.44.0 — fixed in 1.107.6, 2.44.0

How to fix

Upgrade to a fixed version: pydantic-ai 1.107.6, 2.44.0. Check the vendor advisory for mitigations.

References

• https://github.com/pydantic/pydantic-ai/commit/2faa6181d8a17d83bc9516d035c5270db8730fa0
• https://github.com/pydantic/pydantic-ai/commit/9cdc952e4c3319e85a3e04f2de49fbbb765bd38b
• https://github.com/pydantic/pydantic-ai/commit/a93ea5226be1e93ae13131ae3f22287190411389
• https://github.com/pydantic/pydantic-ai/commit/c3fd1cc1f15fdbf750d78e4e3ec1e8b4d6a3d920
• https://github.com/pydantic/pydantic-ai/commit/fb92ccfc3ca2735dab877e2ed73856681bf72ad1
• https://github.com/pydantic/pydantic-ai/pull/8397
• https://github.com/pydantic/pydantic-ai/pull/8399
• https://github.com/pydantic/pydantic-ai/pull/8418
• https://github.com/pydantic/pydantic-ai/pull/84332
• https://github.com/pydantic/pydantic-ai/pull/8434
• https://github.com/pydantic/pydantic-ai/releases/tag/v1.107.6
• https://github.com/pydantic/pydantic-ai/releases/tag/v2.44.0

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