CVE-2026-109239 in Crawl4AI
Summary
by MITRE • 10/12/2026
Crawl4AI before 0.9.4 contains a blind server-side request forgery vulnerability in RobotsParser.can_fetch that lets unauthenticated attackers bypass Docker server egress controls. Attackers can enable check_robots_txt and use redirects or DNS rebinding to reach internal, loopback, or cloud-metadata addresses for service discovery.
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Analysis
by VulDB Data Team • 10/12/2026
Crawl4AI versions prior to 0.9.4 are susceptible to a blind Server-Side Request Forgery vulnerability located within the RobotsParser.can_fetch function. This flaw arises from insufficient validation of user-supplied input when processing robots.txt directives, allowing unauthenticated attackers to manipulate the target URL used for outbound HTTP requests initiated by the server-side application logic. The core technical deficiency lies in the parser's ability to follow redirects and resolve DNS records without adequate restrictions on destination addresses or protocols. By leveraging standard web mechanisms such as HTTP 3xx redirections or exploiting DNS rebinding techniques, an attacker can redirect the internal request from a public-facing endpoint to arbitrary internal network resources that are typically inaccessible from external networks.
The operational impact of this vulnerability is significant because it effectively bypasses Docker server egress controls and other perimeter security measures designed to restrict outbound traffic. Attackers can utilize this capability for service discovery within the host environment or connected cloud infrastructure. Specifically, by directing requests toward loopback addresses such as 127.0.0.1 or internal API endpoints, adversaries can probe for running services like databases, message queues, or management interfaces that are not exposed to the public internet but remain reachable from within the containerized environment. Furthermore, access to cloud-metadata addresses allows attackers to retrieve sensitive instance metadata, including authentication tokens and configuration details, which can lead to full compromise of the underlying infrastructure if combined with other exploitation techniques.
This vulnerability aligns with Common Weakness Enumeration CWE-918, which describes Server-Side Request Forgery (SSRF), specifically highlighting the failure to validate server-side requests against a list of allowed destinations or protocols. In terms of offensive security frameworks, this behavior maps directly to MITRE ATT&CK technique T1504.002, known as Web Service Discovery via Cloud Metadata Services, and potentially T1071.001 for Application Layer Protocol: Web Protocols when used in conjunction with HTTP redirects. The blind nature of the SSRF means that direct response data may not be returned to the attacker immediately, but side-channel effects or subsequent requests can reveal information about internal services.
To mitigate this vulnerability, organizations should upgrade Crawl4AI to version 0.9.4 or later where these input validation checks have been strengthened. In environments where upgrading is not immediately feasible, defensive measures include implementing strict egress filtering at the network level to block outbound connections to private IP ranges and cloud metadata endpoints from containerized workloads unless explicitly required for business logic. Additionally, application-level mitigations involve whitelisting allowed domains in the robots.txt parser configuration rather than relying on blacklist approaches, ensuring that only known safe hosts can be queried. Enforcing DNS resolution restrictions within the Docker runtime environment further reduces the attack surface by preventing DNS rebinding attacks and limiting name resolution to internal trusted resolvers only.