CVE-2026-107287 Pydantic AI: Excessive resource use when local web fetching converts nested HTML
Attackers can cause excessive CPU and memory consumption in Pydantic AI via deeply nested HTML during local web fetching, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-107287?
CVE-2026-107287 is a medium-severity denial of service vulnerability in pydantic-ai, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Which versions are affected by CVE-2026-107287?
10 open source packages ship an affected version, including pydantic-ai and pydantic-ai-slim. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pydantic-ai PyPI | From 1.77.0 | 1.107.7, 2.52.0 |
pydantic-ai PyPI | From 1.77.0 | 1.107.7 |
pydantic-ai PyPI | From 1.77.0 | 1.107.7 |
pydantic-ai PyPI | From 2.0.0b1 | 2.52.0 |
pydantic-ai PyPI | From 2.0.0b1 | 2.52.0 |
pydantic-ai-slim PyPI | From 1.77.0 | 1.107.7, 2.52.0 |
4 more packages
pydantic-ai-slim PyPI | From 1.77.0 | 1.107.7 |
pydantic-ai-slim PyPI | From 1.77.0 | 1.107.7 |
pydantic-ai-slim PyPI | From 2.0.0b1 | 2.52.0 |
pydantic-ai-slim PyPI | From 2.0.0b1 | 2.52.0 |
Products include Pydantic Pydantic Ai.
How do I fix CVE-2026-107287?
Upgrade pydantic-ai to a fixed version for your release line: 1.107.7 or 2.52.0.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-107287 being exploited?
There is no known exploitation of CVE-2026-107287 in the wild and no public exploit code.
Other vulnerabilities in pydantic-ai
- CVE-2026-25580 Pydantic AI Affected by Server-Side Request Forgery (SSRF) in URL Download Handling
- CVE-2026-107295 Pydantic AI Web chat UI (`Agent.to_web()`, `clai web`): a website visited by the developer can trigger agent runs and server-side tool execution on the local chat endpoint
- CVE-2026-107286 Pydantic AI: Concurrency-limited models can keep their slot when a streamed request ends early
- CVE-2026-25640 Pydantic AI affected by Stored XSS via Path Traversal in Web UI CDN URL
- CVE-2026-107289 Pydantic AI: SSRF cloud-metadata blocklist bypass via IPv6 zone identifiers
Sources
Also known as CLEANSTART-2026-HS78493, GHSA-v36g-jcw9-x7cw, PYSEC-2026-4281, PYSEC-2026-4290.