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Pydantic AI: Excessive resource use when local web fetching converts nested HTML

as of Oct 8, 2026 · applies to pydantic-ai >= 1.77.0, < 1.107.7; pydantic-ai >= 2.0.0b1, < 2.52.0 · canonical · codexguild.com/kb/ghsa-v36g-jcw9-x7cw · exported 2026-10-11

Canonical as of Oct 8, 2026

Pydantic AI: Excessive resource use when local web fetching converts nested HTML

Medium severity. Affects pydantic-ai >= 1.77.0, < 1.107.7; pydantic-ai >= 2.0.0b1, < 2.52.0. Upgrade to 1.107.7 / 2.52.0 or later.

CVE-2026-107287 / GHSA-v36g-jcw9-x7cw · severity: medium · CVSS 6.5 · PyPI

Affected

pydantic-ai >= 1.77.0, < 1.107.7 → fixed in 1.107.7
pydantic-ai >= 2.0.0b1, < 2.52.0 → fixed in 2.52.0

Details

Summary

Applications using Pydantic AI's local web-fetch tool can experience excessive CPU and memory use when it converts attacker-controlled HTML. An agent must fetch the affected page; provider-native web fetching is not affected.

Details

Nested block elements cause HTML-to-Markdown conversion to reprocess accumulated text at each level and can greatly expand the intermediate output. The response-body limit bounds downloaded bytes, while the returned-content limit is applied only after conversion. On current releases, conversion runs in a worker thread but can still consume substantial resources and delay other work in the process. Older releases performed conversion on the event loop.

Mitigation

Upgrade to a patched release of pydantic-ai or pydantic-ai-slim. If you cannot upgrade yet, avoid using local web fetching for attacker-controlled HTML.

Source: GHSA-v36g-jcw9-x7cw — GitHub Advisory Database (CC-BY-4.0).