Pydantic AI: Excessive resource use when local web fetching converts nested HTML
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.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pydantic-ai | >= 1.77.0, < 1.107.7, >= 2.0.0b1, < 2.52.0 | 1.107.7, 2.52.0 |
| Python (PyPI) | pydantic-ai-slim | >= 1.77.0, < 1.107.7, >= 2.0.0b1, < 2.52.0 | 1.107.7, 2.52.0 |
References
- https://github.com/pydantic/pydantic-ai/security/advisories/GHSA-v36g-jcw9-x7cw
- https://github.com/pydantic/pydantic-ai/pull/8984
- https://github.com/pydantic/pydantic-ai/pull/8985
- https://github.com/pydantic/pydantic-ai/commit/2b247add4950bef61d352e7ca8aefbd20539180c
- https://github.com/pydantic/pydantic-ai/commit/2fd38792693da00a3ca5412aeffb436787af3545
- https://github.com/pydantic/pydantic-ai
- https://github.com/pydantic/pydantic-ai/releases/tag/v1.107.7
- https://github.com/pydantic/pydantic-ai/releases/tag/v2.52.0
- https://pypi.org/project/pydantic-ai
- https://github.com/advisories/GHSA-v36g-jcw9-x7cw
- https://nvd.nist.gov/vuln/detail/CVE-2026-107287
- https://pypi.org/project/pydantic-ai-slim
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-400, CWE-407- Platform
- Python (PyPI)
- Package
pydantic-ai, pydantic-ai-slim- Disclosed
- 08.10.2026
- Updated
- 15.10.2026 18:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-4281 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-v36g-jcw9-x7cw - CC BY 4.0
OSV / GitHub Advisory Database - PYSEC-2026-4290 - PyPA Advisory Database; CC BY 4.0
Vulnerability history: pydantic-ai
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 14
- First → latest
- 02.2026 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 4
- Medium 8
- Low 2
Disclosures per year
- 2026: 14
-
Pydantic AI: Excessive resource use when local web fetching converts nested HTML this entry
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.