CVE-2026-53754 in crawl4ai
Summary
by MITRE • 06/23/2026
Crawl4AI is an open-source LLM friendly web crawler & scraper. Prior to 0.8.8, the Docker API server's SSRF protection (validate_webhook_url / validate_url_destination in deploy/docker/utils.py) used an explicit IPv4/IPv6 CIDR blocklist that missed several address families. An attacker could reach internal services and cloud metadata endpoints (e.g. 169.254.169.254) despite the filter by encoding an internal IPv4 address inside an IPv6 transition form, or by using the IPv6 unspecified address. Because the Docker API is unauthenticated by default (jwt_enabled: false), no credentials are required. This vulnerability is fixed in 0.8.8.
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Analysis
by VulDB Data Team • 06/24/2026
The vulnerability in Crawl4AI versions prior to 0.8.8 represents a critical server-side request forgery flaw that undermines the security of the Docker API server implementation. This issue stems from inadequate network address validation mechanisms within the web hook URL and URL destination validation functions located in deploy/docker/utils.py. The protection mechanism relied on explicit CIDR blocklists for IPv4 and IPv6 addresses, which created significant gaps in coverage by failing to account for various IPv6 transition mechanisms and address families that could bypass the intended restrictions.
The technical exploitation of this vulnerability occurs through sophisticated encoding techniques that leverage IPv6 transition mechanisms to conceal internal IPv4 addresses within IPv6 address formats. Attackers can utilize IPv6 unspecified addresses or embed internal IPv4 addresses within IPv6 transition constructs to reach services that should remain isolated from external access. This approach specifically targets cloud metadata endpoints such as the widely known 169.254.169.254 address, which serves as the default route for cloud provider instance metadata services and contains sensitive operational data including access keys, instance identifiers, and configuration information.
The operational impact of this vulnerability is severe given that the Docker API server operates unauthenticated by default with jwt_enabled set to false, eliminating any credential-based access controls. This means that any external party can directly exploit the SSRF vulnerability without requiring authentication, potentially leading to unauthorized access to internal services, cloud metadata exposure, and subsequent lateral movement within network environments. The flaw essentially provides an unrestricted pathway for attackers to probe and interact with internal infrastructure that should remain protected behind firewall boundaries.
The vulnerability aligns with CWE-918, which specifically addresses Server-Side Request Forgery vulnerabilities in web applications, and demonstrates characteristics consistent with ATT&CK technique T1071.004 for application layer protocol tunneling. The implementation flaw represents a classic case of insufficient input validation where the security controls fail to properly sanitize network address representations, allowing malicious actors to bypass intended network isolation boundaries. Organizations using Crawl4AI versions before 0.8.8 should immediately implement mitigations including updating to the patched version, enabling authentication mechanisms, and deploying network segmentation controls to prevent unauthorized access to internal services.
The fix implemented in version 0.8.8 addresses this vulnerability by expanding the CIDR blocklist to include comprehensive coverage of all relevant IPv6 address families and transition mechanisms while also strengthening the validation logic to properly handle various address encoding formats. This remediation ensures that all internal network addresses including those accessible via IPv6 transition techniques are properly blocked, preventing access to sensitive metadata endpoints and internal services that should remain isolated from external network access. The update demonstrates the importance of thorough network address validation in security implementations and highlights the need for comprehensive testing of edge cases in protocol handling functions.