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[ CVE-2026-107290 · Published 8 Oct 2026 ]

Pydantic AI: Event loop blocked by quadratic title extraction in `web_fetch`

CVSS 6.5 EPSS <1%Fix available

[ Description ]Official 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.

[ Fixes ]Fixes and patches

  • pydantic-ai 1.107.6Fixed version · GitHub Advisories · pip package pydantic-ai: upgrade to 1.107.6 or later (affected >= 1.77.0, < 1.107.6)
  • pydantic-ai 2.44.0Fixed version · GitHub Advisories · pip package pydantic-ai: upgrade to 2.44.0 or later (affected >= 2.0.0b1, < 2.44.0)
  • pydantic-ai-slim 1.107.6Fixed version · GitHub Advisories · pip package pydantic-ai-slim: upgrade to 1.107.6 or later (affected >= 1.77.0, < 1.107.6)
  • pydantic-ai-slim 2.44.0Fixed version · GitHub Advisories · pip package pydantic-ai-slim: upgrade to 2.44.0 or later (affected >= 2.0.0b1, < 2.44.0)
  • Patch on github.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD
  • Patch on github.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD
  • Patch on github.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD
  • Patch on github.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD

[ Packages ]Affected open-source packages

[ References ]References