🛡️ Sentinel: [CRITICAL] Fix SSRF in web_fetch

[mudcube]

🚨 Severity: CRITICAL
💡 Vulnerability: The web_fetch tool in mill-plugin-system used reqwest::blocking::get directly without IP validation, allowing Server-Side Request Forgery (SSRF) where attackers could reach internal or private network services.
🎯 Impact: Attackers could access internal infrastructure, query cloud metadata services, and scan internal networks from the TypeMill server.
🔧 Fix: Replaced direct get with an iterative IP resolution and validation loop:

• Resolves target hostname into all its IP addresses via std::net::ToSocketAddrs.
• Validates every IP using a robust custom is_allowed_ip check, explicitly failing if loopback, private, unspecified, or local subnets (both IPv4 and IPv6 mapped) are returned.
• Mitigates DNS Rebinding attacks by passing the validated IP directly to reqwest using .resolve(host, pinned_ip), pinning the connection without breaking SNI.
• Mitigates indirect SSRF via HTTP redirects by disabling automatic redirects and implementing a secure tracking loop that resolves and validates redirect targets sequentially.
  ✅ Verification: Hand-tested with malicious local inputs (e.g., 127.0.0.1, 0.0.0.0), ran cargo check, cargo test -p mill-plugin-system, and linted cleanly. Added to .jules/sentinel.md journal.

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PR created automatically by Jules for task 8098961338877017312 started by @mudcube

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Block shared internal IPv4 ranges

Because this fall-through allows every IPv4 address not explicitly listed, web_fetch still permits non-public ranges such as 100.64.0.0/10 and 198.18.0.0/15. In deployments that use those ranges for VPC/container/internal services, an attacker can fetch http://100.64.x.y/... and bypass the SSRF protection even though the address is not globally routable; the allowlist should reject all special-use/non-global ranges, not just RFC1918/link-local.

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