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6.5

Pydantic AI can stall when processing crafted web pages

CVE-2026-107290 · published 27 days ago
Summary

Versions of Pydantic AI up to 1.107.5 and 2.43.9 may get stuck while extracting titles from a maliciously crafted web page, causing the system to pause other tasks. The problem also appears when the page contains unsupported media types or deeply nested HTML/JSON, which can stop a single run. Upgrade to version 1.107.6 or later, or 2.44.0 or later, to prevent the slowdown and ensure normal operation.

What to do
  • Update douwe maan pydantic-ai to version 1.107.6.
  • Update douwe maan pydantic-ai to version 2.44.0.
  • Update douwe maan pydantic-ai-slim to version 1.107.6.
  • Update douwe maan pydantic-ai-slim to version 2.44.0.
  • Update pydantic-ai to version 1.107.6.
  • Update pydantic-ai to version 2.44.0.
  • Update pydantic-ai-slim to version 1.107.6.
  • Update pydantic-ai-slim to version 2.44.0.
Affected software
Ecosystem VendorProductAffected versions
pip douwe maan pydantic-ai >= 1.77.0, < 1.107.6
>= 2.0.0b1, < 2.44.0
Fix: upgrade to 1.107.6
pip douwe maan pydantic-ai-slim >= 1.77.0, < 1.107.6
>= 2.0.0b1, < 2.44.0
Fix: upgrade to 1.107.6
pip – pydantic-ai >= 1.77.0, < 1.107.6
>= 2.0.0b1, < 2.44.0
Fix: upgrade to 1.107.6
pip – pydantic-ai-slim >= 1.77.0, < 1.107.6
>= 2.0.0b1, < 2.44.0
Fix: upgrade to 1.107.6
– pydantic pydantic_ai >= 1.77.0, < 1.107.6
>= 2.0.0, < 2.44.0
cpe:2.3:a:pydantic:pydantic_ai:*:*:*:*:*:python:*:*
Original advisory text
Pydantic AI: Event loop blocked by quadratic title extraction in `web_fetch`
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.
References
Fix within
Internet-facing 60 days
Internal At next upgrade
  • Not known to be exploited
  • Needs hands-on effort to exploit
  • Gives an attacker partial control
Severity
6.5 Medium
Exploitation
<1% chance of attack within 30 days
Type
CWE-1333Inefficient Regular Expression Complexity (ReDoS)
CWE-407Inefficient Algorithmic Complexity
Timeline
Published8 Oct 2026
Updated4 Nov 2026
First seen8 Oct 2026
Sources
CVE-2026-107290 · NVD
GHSA-fpf4-vwcp-v4hp · GHSA
CVE-2026-107290 · OSV
GHSA-fpf4-vwcp-v4hp · OSV
PYSEC-2026-4277 · OSV
PYSEC-2026-4286 · OSV
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