CVE-2026-56266 Overview
CVE-2026-56266 is a Server-Side Request Forgery (SSRF) vulnerability [CWE-918] in Crawl4AI versions before 0.8.7. The flaw resides in the /crawl, /crawl/stream, /md, and /llm endpoints, which fetch arbitrary user-supplied URLs without proper validation. Unauthenticated attackers can bypass the application's internal-address blocklist by submitting IPv6-mapped IPv4 addresses. This bypass allows requests to reach internal services and cloud metadata endpoints from the server hosting Crawl4AI. Successful exploitation can lead to disclosure of cloud provider credentials, internal API responses, and other sensitive data accessible from the server's network position.
Critical Impact
Unauthenticated attackers can exfiltrate cloud metadata credentials and pivot into internal networks by abusing IPv6-mapped IPv4 address parsing.
Affected Products
- Crawl4AI versions prior to 0.8.7
- Deployments exposing the /crawl, /crawl/stream, /md, or /llm HTTP endpoints
- Cloud-hosted Crawl4AI instances with access to instance metadata services (IMDS)
Discovery Timeline
- 2026-06-22 - CVE-2026-56266 published to the National Vulnerability Database
- 2026-06-23 - Last updated in NVD database
Technical Details for CVE-2026-56266
Vulnerability Analysis
Crawl4AI exposes HTTP endpoints that accept a target URL and fetch it server-side. The application implements a blocklist intended to prevent requests to internal address ranges such as 127.0.0.0/8, 10.0.0.0/8, and link-local metadata addresses like 169.254.169.254. The blocklist evaluates the supplied host using string or IPv4 representations only. When an attacker submits an IPv6-mapped IPv4 address such as [::ffff:127.0.0.1] or [::ffff:a9fe:a9fe], the validation logic fails to recognize the embedded IPv4 address. The underlying HTTP client then resolves and connects to the mapped IPv4 destination, completing the request to the restricted resource.
Root Cause
The root cause is incomplete input validation in the URL filtering layer. The blocklist normalizes hostnames as IPv4 or DNS strings but does not canonicalize IPv6 representations that embed IPv4 addresses under the ::ffff:0:0/96 prefix defined in RFC 4291. Because Python socket libraries and most HTTP stacks transparently route these mapped addresses to the IPv4 stack, the request reaches the internal target despite the filter.
Attack Vector
The attack vector is unauthenticated network access to any of the four vulnerable endpoints. An attacker sends a POST or GET request containing a URL with an IPv6-mapped IPv4 host targeting an internal resource. The Crawl4AI server fetches the URL and returns the response body in its rendered output. In cloud environments, attackers can target [::ffff:169.254.169.254] to retrieve instance metadata, IAM role tokens, or user-data scripts.
No verified exploit code is published. Technical details are available in the GitHub Security Advisory GHSA-365w-hqf6-vxfg and the VulnCheck SSRF Advisory.
Detection Methods for CVE-2026-56266
Indicators of Compromise
- Inbound HTTP requests to /crawl, /crawl/stream, /md, or /llm containing URLs with [::ffff: host components
- Outbound connections from the Crawl4AI host to 169.254.169.254, 127.0.0.1, or RFC 1918 ranges shortly after API requests
- Unexpected access to cloud instance metadata service tokens originating from the Crawl4AI service account
Detection Strategies
- Inspect application access logs for URL parameters containing IPv6-mapped IPv4 notation, percent-encoded brackets, or hex-encoded loopback addresses
- Correlate Crawl4AI request timestamps with egress flows to internal CIDR ranges using network flow telemetry
- Alert on any process owned by the Crawl4AI service issuing requests to 169.254.169.254 or other metadata endpoints
Monitoring Recommendations
- Enable verbose request logging on the Crawl4AI service and forward logs to a centralized analytics platform
- Monitor cloud audit logs for unexpected use of IAM role credentials tied to the Crawl4AI host
- Implement egress filtering alerts that trigger on outbound traffic to link-local, loopback, or private network ranges
How to Mitigate CVE-2026-56266
Immediate Actions Required
- Upgrade Crawl4AI to version 0.8.7 or later across all deployments
- Restrict public exposure of the /crawl, /crawl/stream, /md, and /llm endpoints behind authentication and network ACLs
- Apply IMDSv2 with hop-limit enforcement on AWS instances, or equivalent metadata hardening on Azure and GCP
Patch Information
The maintainers released a fix in Crawl4AI 0.8.7. The patch is referenced in the GitHub Security Advisory GHSA-365w-hqf6-vxfg. Source code and release notes are available in the Crawl4AI GitHub repository.
Workarounds
- Deploy a reverse proxy or web application firewall that rejects URLs containing ::ffff: or other IPv6-mapped IPv4 notations
- Enforce egress network policies blocking the Crawl4AI host from reaching 169.254.169.254, 127.0.0.0/8, 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16
- Run Crawl4AI in an isolated network segment without access to cloud metadata services or internal management interfaces
# Example egress restriction using iptables to block metadata and private ranges
iptables -A OUTPUT -d 169.254.169.254 -j DROP
iptables -A OUTPUT -d 127.0.0.0/8 -j DROP
iptables -A OUTPUT -d 10.0.0.0/8 -j DROP
iptables -A OUTPUT -d 172.16.0.0/12 -j DROP
iptables -A OUTPUT -d 192.168.0.0/16 -j DROP
# Block IPv6-mapped IPv4 metadata equivalent
ip6tables -A OUTPUT -d ::ffff:169.254.169.254 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
