CVE-2026-56264: Crawl4AI - Arbitrary JavaScript Execution via /execute_js Endpoint

Synopsis

Arbitrary JavaScript execution vulnerability in Crawl4AI's Docker API server allows unauthenticated remote attackers to submit and run arbitrary JavaScript through the /execute_js endpoint. The browser context runs with --disable-web-security enabled, removing same-origin protections and making internal network services directly reachable from the browser. Successful exploitation gives an attacker full read and write access to data the browser can reach and enables server-side request forgery against internal services. A patched-image rebuild at version 0.8.7 is available on HarborGuard for environments running an affected version.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the Crawl4AI Docker API server over the network; any internet- or LAN-exposed instance of the service is directly targetable.

• AuthenticationNot required

  The /execute_js endpoint requires no credentials, so any client that can reach the service can submit arbitrary JavaScript for execution.

• Victim interactionNot required

  No user action is needed; the attacker sends a direct API request and the server executes the payload without any human interaction on the target side.

• Attack complexityDetail

  Exploitation involves elevated complexity due to attack requirements (AT:P) and environmental factors (AC:H), such as specific browser context conditions or timing dependencies, meaning the exploit is not unconditionally reliable on first attempt.

Blast Radius

• Reads any data accessible to the browser context, including responses from internal services reached via server-side request forgery, such as metadata APIs, internal dashboards, or credential endpoints.
• Modifies state on internal services by issuing authenticated-by-network requests from the server's browser, including writing data to APIs that trust the server's network origin.
• Crashes or disrupts the Crawl4AI service process by exhausting browser resources or triggering unhandled exceptions in the JavaScript runtime.
• Exfiltrates secrets available to the browser environment, such as tokens injected into the page context or environment variables accessible via JavaScript APIs exposed in the --disable-web-security configuration.