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CVE-2026-53754 – SSRF Filter Bypass – Crawl4AI Docker API Server prior to 0.8.8

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Summary

CVE-2026-53754 is a Server-Side Request Forgery (SSRF) filter bypass vulnerability in the Crawl4AI Docker API server affecting all versions prior to 0.8.8. The flaw allows unauthenticated, network-based attackers to bypass the built-in SSRF protection and reach internal services and cloud metadata endpoints, potentially exposing cloud credentials. The vulnerability is rated High (CVSS 7.5) with no authentication, user interaction, or elevated privileges required.

Technical details

  • Root cause: The SSRF protection functions validate_webhook_url and validate_url_destination in deploy/docker/utils.py implemented an explicit IPv4/IPv6 CIDR blocklist that failed to account for several IPv6 address families and transition mechanisms.
  • Trigger conditions: An attacker submits a crafted URL to any API endpoint that accepts a destination URL (e.g., /crawl, webhook parameters). The blocklist check is evaluated before the HTTP request is dispatched.
  • Bypass techniques: The filter can be circumvented by encoding a blocked internal IPv4 address in any of the following forms, all of which resolve to the same internal address without triggering the blocklist:
    • IPv4-mapped IPv6 address (e.g., ::ffff:169.254.169.254)
    • NAT64 transition address (e.g., 64:ff9b::a9fe:a9fe)
    • 6to4 transition address (e.g., 2002:a9fe:a9fe::)
    • IPv6 unspecified address (::)
  • Authentication bypass: The Docker API server ships with jwt_enabled: false by default in versions prior to 0.9.0, meaning no credentials are required to interact with any API endpoint. The server binds on port 11235.
  • Impact: Successful exploitation enables SSRF to internal network services and cloud instance metadata endpoints (e.g., 169.254.169.254), allowing an attacker to retrieve cloud provider credentials (AWS, GCP, Azure) and access other internal resources not intended to be publicly reachable.
  • Fix: The patch replaces the blocklist approach with a single rule: reject any resolved IP address where not ip.is_global, applied to both primary resolved addresses and any embedded IPv4 form within transition addresses.

Affected software

  • Crawl4AI (Docker API server) — all versions prior to 0.8.8 (i.e., ≤ 0.8.7)

Severity

  • CVSS v3.1 Base Score: 7.5 (High)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Mitigation and recommended actions

  • Immediate action: Upgrade Crawl4AI to version 0.8.8 or later, which contains the vendor-provided fix.
  • Network mitigation (if patching is not immediately possible):
    • Restrict access to port 11235 at the network or firewall level so that the Docker API is not reachable from untrusted networks.
    • Avoid exposing the Crawl4AI Docker API directly to the public internet; place it behind an authenticated reverse proxy.
    • If running on a cloud instance, ensure instance metadata service access from the container is restricted (e.g., via IMDSv2 enforcement on AWS, or equivalent controls on GCP/Azure).

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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