fix: close SSRF IPv6 bypass and replace Math.random() session IDs with crypto.randomUUID()

[Copilot]

Summary

Two security vulnerabilities in the SSRF guard and session ID generation. The SSRF filter missed IPv4-mapped IPv6 addresses entirely, and session IDs relied on Math.random() — a non-CSPRNG source.

Related Issues

Changes

• lib/server/ssrf-guard.ts

  • Added extractIPv4FromMappedIPv6() to unwrap both dotted-decimal (::ffff:127.0.0.1) and hex-encoded (::ffff:7f00:1) IPv4-mapped IPv6 addresses, then validates the embedded IPv4 against existing private-range rules
  • Scoped all IPv6 range checks (unique-local fc00::/7, link-local fe80::/10, loopback) to hostnames containing : — prevents false-positive blocks on domain names like fdomain.com
  • Split isBlockedHostname into isBlockedIPv4 + isBlockedHostname for clarity and reuse

• components/chat/use-chat-sessions.ts

  • Replaced all three \session-${Date.now()}-${Math.random()...}`session ID patterns with`session-${crypto.randomUUID()}``

// Before — predictable
const sessionId = `session-${Date.now()}-${Math.random().toString(36).slice(2)}`;

// After — CSPRNG-backed
const sessionId = `session-${crypto.randomUUID()}`;

// Before — missed IPv4-mapped IPv6
hostname === '::1' || hostname === 'localhost' || ...

// After — unwraps ::ffff:7f00:1 → 127.0.0.1 before range checks
const embeddedIPv4 = extractIPv4FromMappedIPv6(hostname);
if (embeddedIPv4 !== null) {
  if (isBlockedIPv4(embeddedIPv4)) return 'Local/private network URLs are not allowed';
  return null;
}

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Verification

Steps to reproduce / test

1. Supply http://[::ffff:127.0.0.1]/ as a custom base URL — previously bypassed the SSRF guard, now blocked
2. Supply http://[::ffff:7f00:1]/ — same bypass, now blocked
3. Supply https://api.openai.com — passes through correctly
4. Supply http://fdomain.com — passes through (no false positive on fd-prefixed domain)

What you personally verified

• SSRF guard correctly blocks all private-range IPv4-mapped IPv6 variants
• No false positives on legitimate domain names starting with fd, fc, fe80, etc.
• crypto.randomUUID() is available in both browser and Node.js (Next.js) runtimes

Evidence

• CI passes (pnpm check && pnpm lint && npx tsc --noEmit)
• Manually tested locally
• Screenshots / recordings attached (if UI changes)

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have added/updated documentation as needed
• My changes do not introduce new warnings