CVE-2026-56264: Crawl4AI RCE Vulnerability

CVE-2026-56264 Overview

CVE-2026-56264 is an arbitrary JavaScript execution vulnerability in Crawl4AI versions before 0.8.7. The flaw resides in the Docker API server's /execute_js endpoint, which accepts and runs user-supplied JavaScript inside the server's browser context. The browser runs with the --disable-web-security flag enabled, removing same-origin policy protections. Unauthenticated attackers with network access can execute arbitrary JavaScript and pivot to server-side request forgery (SSRF) against internal services. The vulnerability is tracked under CWE-94: Improper Control of Generation of Code.

Critical Impact
Unauthenticated attackers can execute arbitrary JavaScript in the Crawl4AI browser context and reach internal network services via SSRF, exposing cloud metadata endpoints and internal APIs.

Affected Products

Crawl4AI Docker API server versions prior to 0.8.7
Deployments exposing the /execute_js endpoint over a network
Crawl4AI instances running Chromium with --disable-web-security enabled

Discovery Timeline

2026-06-30 - CVE-2026-56264 published to the National Vulnerability Database
2026-07-01 - Last updated in NVD database

Technical Details for CVE-2026-56264

Vulnerability Analysis

Crawl4AI ships a Docker-based API server that exposes an /execute_js endpoint. The endpoint is designed to run JavaScript inside a headless Chromium instance to support dynamic web scraping. The implementation accepts JavaScript payloads from API clients and executes them directly in the browser context without sandboxing or validation.

The underlying Chromium instance is launched with --disable-web-security, which disables the same-origin policy (SOP) and cross-origin resource sharing (CORS) enforcement. This design decision removes the browser's core isolation boundary between origins. As a result, JavaScript submitted through the endpoint can issue cross-origin HTTP requests and read the responses.

Root Cause

The root cause is twofold. First, the endpoint treats user-supplied JavaScript as trusted input and passes it directly to a browser evaluation function. Second, the browser is intentionally configured to bypass web security controls. These two design choices combine to convert the API into a remote JavaScript execution primitive with no origin restrictions.

Attack Vector

An attacker sends an HTTP request to the /execute_js endpoint containing arbitrary JavaScript. The browser executes the code within its process context. Because SOP is disabled, the attacker can issue fetch() or XMLHttpRequest calls to internal-only endpoints, including cloud instance metadata services such as 169.254.169.254, internal Kubernetes APIs, and unauthenticated administrative interfaces on the same network segment. Response bodies are returned to the attacker via the endpoint's execution result.

Code examples are not published in the enriched data. See the GitHub Security Advisory GHSA-365w-hqf6-vxfg and the VulnCheck Advisory for technical details.

Detection Methods for CVE-2026-56264

Indicators of Compromise

HTTP POST requests to /execute_js on Crawl4AI Docker API servers from unexpected source addresses
Outbound requests from the Crawl4AI container to 169.254.169.254, metadata.google.internal, or other cloud metadata endpoints
Outbound connections from the Crawl4AI container to internal RFC1918 addresses that are not part of normal scraping targets
JavaScript payloads in API request bodies containing fetch(, XMLHttpRequest, or references to internal hostnames

Detection Strategies

Inspect reverse proxy and API gateway logs for calls to the /execute_js route and flag anomalous request volumes or non-scraping payloads
Correlate /execute_js requests with subsequent outbound network flows from the Crawl4AI container using network telemetry
Alert on any egress from scraping infrastructure to link-local or metadata service IP ranges

Monitoring Recommendations

Enable verbose access logging on the Crawl4AI Docker API server and forward logs to a centralized SIEM
Deploy egress network policies with logging on the container namespace to capture destination IPs and ports
Track Crawl4AI container version metadata to identify hosts still running versions below 0.8.7

How to Mitigate CVE-2026-56264

Immediate Actions Required

Upgrade Crawl4AI to version 0.8.7 or later on all Docker API server deployments
Restrict network access to the Crawl4AI API to trusted client IPs using firewall rules or a reverse proxy allowlist
Require authentication on the /execute_js endpoint and disable it entirely if not required by workloads
Audit recent access logs for unauthorized calls to /execute_js and investigate outbound traffic from affected containers

Patch Information

The maintainers addressed the vulnerability in Crawl4AI 0.8.7. Users should pull the updated container image from the Crawl4AI GitHub repository and redeploy. Review the GitHub Security Advisory GHSA-365w-hqf6-vxfg for full remediation guidance.

Workarounds

Place the Crawl4AI API behind an authenticating reverse proxy that blocks unauthenticated access to /execute_js
Run the Crawl4AI container in an isolated network segment with egress restricted to public internet destinations only, blocking RFC1918 and link-local ranges
Remove the --disable-web-security flag from the browser launch configuration if custom builds are in use
Disable or remove the /execute_js route if the JavaScript execution feature is not required

bash

# Example egress restriction for the Crawl4AI container (iptables)
iptables -I DOCKER-USER -s <crawl4ai_container_ip> -d 169.254.169.254 -j DROP
iptables -I DOCKER-USER -s <crawl4ai_container_ip> -d 10.0.0.0/8 -j DROP
iptables -I DOCKER-USER -s <crawl4ai_container_ip> -d 172.16.0.0/12 -j DROP
iptables -I DOCKER-USER -s <crawl4ai_container_ip> -d 192.168.0.0/16 -j DROP