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CVE-2026-91941 – Denial of Service (Uncontrolled Resource Consumption) – Crawl4AI before 0.9.3

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Summary

CVE-2026-91941 is an uncontrolled resource consumption vulnerability (denial of service) affecting Crawl4AI, an open-source LLM-friendly web crawler and scraper, in versions prior to 0.9.3. The flaw resides in the PDFContentScrapingStrategy component used by Crawl4AI’s Docker API, allowing untrusted, unauthenticated clients to trigger resource exhaustion on the server. The vulnerability has a High severity rating (CVSS 8.7 / CVSS v3.1 7.5), with no authentication or user interaction required to exploit.

Technical details

  • Root cause: When PDFContentScrapingStrategy is selected, Crawl4AI downloads and processes a remote PDF specified by the client without enforcing any limit on file size, page count, or processing time.
  • Trigger conditions: An attacker submits a POST request to the Crawl4AI Docker API selecting the PDF scraping strategy and pointing it at a large or many-page remote PDF file.
  • Attack vector: Network-based, requires no privileges and no user interaction (CVSS AV:N/AC:L/PR:N/UI:N).
  • Impact: A single malicious request can exhaust disk space, CPU, and bandwidth on shared worker infrastructure, causing denial of service for the crawling service and any co-located workloads. The vulnerability affects availability only — no confidentiality or integrity impact is reported.

Affected software

  • Product: crawl4ai (PyPI package), maintained by unclecode
  • Vulnerable versions: All versions prior to 0.9.3
  • Fixed version: 0.9.3 and later

Severity

  • CVSS v4.0: 8.7 (High) — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
  • CVSS v3.1: 7.5 (High) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Mitigation and recommended actions

  • Immediate: Upgrade Crawl4AI to version 0.9.3 or later, which enforces limits on PDF size, page count, and processing time within PDFContentScrapingStrategy.
  • If immediate patching is not possible:
    • Disable or restrict access to the PDFContentScrapingStrategy option on any internet-facing Crawl4AI Docker API deployment.
    • Place rate limiting and request size restrictions in front of the Crawl4AI API to constrain the size and frequency of crawl requests.
    • Restrict API access to trusted/authenticated clients only, and monitor for abnormal disk, CPU, or bandwidth usage on worker instances handling PDF crawl requests.

References

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