CVE-2026-107287: Pydantic Pydantic-Ai

Medium severity, CVSS 6.5. EPSS: 0.3% chance of exploitation in the next 30 days.

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.

Affected products

• Pydantic Pydantic-Ai: from 1.77.0, before 1.107.7 (fixed in 1.107.7); from 2.0.0b1, before 2.52.0 (fixed in 2.52.0)
• Pydantic Pydantic-Ai-Slim: from 1.77.0, before 1.107.7 (fixed in 1.107.7); from 2.0.0b1, before 2.52.0 (fixed in 2.52.0)

Published 2026-10-08. Last modified 2026-10-08.