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CVE-2026-107290— Pydantic AI: Event loop blocked by quadratic title extraction in `web_fetch`

Quick assessment

Affected
pydantic pydantic-ai
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Pydantic AI 是一个用于构建生成式 AI 应用和工作流的 Python 智能体框架。在版本 1.77.0 至 1.107.6 以及 2.44.0 之前， 和 WebFetch 的本地回退处理服务器端响应时，采用二次复杂度执行标题提取、空白字符规范化以及有序列表编号。因此，攻击者可以构造一个尺寸适中的恶意网页，长时间阻塞事件循环，导致其他智能体运行和请求停滞；同时，不受支持的编码格式或过度的 HTML/JSON 嵌套也可能导致单个智能体运行异常终止。该问题已在版本 1.107.6 和 2.44.0 中得到修

CVSS 6.5 · Medium

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 4

VendorProduct Version RangeStatus
pydantic pydantic-ai >= 1.77.0, < 1.107.6 affected
>= 2.0.0b1, < 2.44.0 affected
pydantic pydantic-ai-slim >= 1.77.0, < 1.107.6 affected
>= 2.0.0b1, < 2.44.0 affected
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I. Basic Information for CVE-2026-107290

Vulnerability Information
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Vulnerability Title
Pydantic AI: Event loop blocked by quadratic title extraction in `web_fetch`
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1333
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
pydantic pydantic-ai >= 1.77.0, < 1.107.6 -
pydantic pydantic-ai-slim >= 1.77.0, < 1.107.6 -

II. Public POCs for CVE-2026-107290

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III. Intelligence Information for CVE-2026-107290

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Vendor Pages for CVE-2026-107290 (2)

Other References for CVE-2026-107290 (11)

Same Patch Batch · pydantic · 2026-10-08 · 10 CVEs total

CVE-2026-107295 7.6 HIGH `pydantic-ai-slim` web UI `/api/chat` accepts browser-simple cross-origin requests that ca
CVE-2026-107286 7.5 HIGH Pydantic AI: Concurrency-limited models can keep their slot when a streamed request ends e
CVE-2026-107289 6.8 MEDIUM Pydantic AI: SSRF cloud-metadata blocklist bypass via IPv6 zone identifier (incomplete fix
CVE-2026-107287 6.5 MEDIUM Pydantic AI: Excessive resource use when local web fetching converts nested HTML
CVE-2026-107294 6.5 MEDIUM Pydantic AI: Unbounded memory use when downloading remote content via web_fetch or FileUrl
CVE-2026-107292 6.4 MEDIUM Pydantic AI Web chat UI (`Agent.to_web()`, `clai web`): the local chat endpoint does not v
CVE-2026-107288 3.7 LOW Pydantic AI: web_fetch_tool blocked_domains bypass via a hostname the resolver normalizes
CVE-2026-107291 2.3 LOW Pydantic AI OpenTelemetry instrumentation: exception events on tool and agent run spans in
CVE-2026-107293 2.3 LOW Pydantic AI OpenTelemetry instrumentation: retry prompt content is not redacted when `incl

IV. Related Vulnerabilities

Same product: pydantic-ai
Same vendor: pydantic
Same weakness: CWE-1333

V. Comments for CVE-2026-107290

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