PYSEC-2026-4290

Vulnerability from pysec - Published: 2026-10-15 10:22 - Updated: 2026-10-15 14:38
VLAI
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.

Severity
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Impacted products
Name purl
pydantic-ai-slim pkg:pypi/pydantic-ai-slim
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "pydantic-ai-slim",
        "purl": "pkg:pypi/pydantic-ai-slim"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.77.0"
            },
            {
              "fixed": "1.107.7"
            },
            {
              "introduced": "2.0.0b1"
            },
            {
              "fixed": "2.52.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.100.0",
        "1.101.0",
        "1.102.0",
        "1.103.0",
        "1.104.0",
        "1.105.0",
        "1.106.0",
        "1.107.0",
        "1.107.1",
        "1.107.2",
        "1.107.4",
        "1.107.5",
        "1.107.6",
        "1.77.0",
        "1.78.0",
        "1.79.0",
        "1.80.0",
        "1.81.0",
        "1.82.0",
        "1.83.0",
        "1.84.0",
        "1.84.1",
        "1.85.0",
        "1.85.1",
        "1.86.0",
        "1.86.1",
        "1.87.0",
        "1.88.0",
        "1.89.0",
        "1.89.1",
        "1.90.0",
        "1.91.0",
        "1.92.0",
        "1.93.0",
        "1.94.0",
        "1.95.0",
        "1.95.1",
        "1.96.0",
        "1.96.1",
        "1.97.0",
        "1.98.0",
        "1.99.0",
        "2.0.0",
        "2.0.0b1",
        "2.0.0b2",
        "2.0.0b3",
        "2.0.0b4",
        "2.0.0b5",
        "2.0.0b6",
        "2.0.0b7",
        "2.1.0",
        "2.10.0",
        "2.11.0",
        "2.12.0",
        "2.13.0",
        "2.14.0",
        "2.14.1",
        "2.15.0",
        "2.16.0",
        "2.17.0",
        "2.18.0",
        "2.19.0",
        "2.2.0",
        "2.20.0",
        "2.21.0",
        "2.22.0",
        "2.23.0",
        "2.24.0",
        "2.25.0",
        "2.26.0",
        "2.27.0",
        "2.27.1",
        "2.28.0",
        "2.29.0",
        "2.3.0",
        "2.30.0",
        "2.31.0",
        "2.31.1",
        "2.32.0",
        "2.32.1",
        "2.32.2",
        "2.33.0",
        "2.34.0",
        "2.35.0",
        "2.35.1",
        "2.35.3",
        "2.36.0",
        "2.37.0",
        "2.38.0",
        "2.39.0",
        "2.4.0",
        "2.40.0",
        "2.41.0",
        "2.42.0",
        "2.43.0",
        "2.44.0",
        "2.45.0",
        "2.46.0",
        "2.47.0",
        "2.48.0",
        "2.49.0",
        "2.5.0",
        "2.5.1",
        "2.50.0",
        "2.51.0",
        "2.6.0",
        "2.7.0",
        "2.8.0",
        "2.9.0",
        "2.9.1"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-107287",
    "GHSA-v36g-jcw9-x7cw"
  ],
  "details": "### Summary\n\nApplications using Pydantic AI\u0027s 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.\n\n### Details\n\nNested 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.\n\n### Mitigation\n\nUpgrade 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.",
  "id": "PYSEC-2026-4290",
  "modified": "2026-10-15T14:38:05.436245Z",
  "published": "2026-10-15T10:22:51.943576Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/pydantic/pydantic-ai/security/advisories/GHSA-v36g-jcw9-x7cw"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pydantic/pydantic-ai/pull/8984"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pydantic/pydantic-ai/pull/8985"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pydantic/pydantic-ai/commit/2b247add4950bef61d352e7ca8aefbd20539180c"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pydantic/pydantic-ai/commit/2fd38792693da00a3ca5412aeffb436787af3545"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/pydantic/pydantic-ai"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pydantic/pydantic-ai/releases/tag/v1.107.7"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pydantic/pydantic-ai/releases/tag/v2.52.0"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/pydantic-ai-slim"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-v36g-jcw9-x7cw"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-107287"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Pydantic AI: Excessive resource use when local web fetching converts nested HTML"
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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Nomenclature

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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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