@utcp/http: SSRF via attacker-controlled OpenAPI servers[0].url in HTTP communication protocol

Summary

The @utcp/http package is vulnerable to a blind Server-Side Request Forgery (SSRF) caused by a trust-boundary inconsistency between manual discovery and tool invocation. registerManual() validates the discovery URL against an HTTPS / loopback allowlist, but callTool() reuses the resolved toolCallTemplate.url directly without revalidating, and the OpenApiConverter blindly trusts whatever servers[0].url an attacker-hosted spec declares. An attacker who hosts a malicious OpenAPI spec on a legitimate HTTPS endpoint can declare e.g. servers: [{ url: "http://127.0.0.1:9090" }] or servers: [{ url: "http://169.254.169.254" }]; the converter then produces tools whose URL points at internal services on the agent host.

A separate prefix-bypass also affected the discovery-time check: the previous startsWith('http://localhost') guard let URLs like http://localhost.evil.com through.

Sister advisory

This is the npm/TypeScript counterpart of GHSA-39j6-4867-gg4w / CVE-2026-44661 on the Python utcp-http package. Same vulnerability, same fix shape, same reporter.

Versions and patch state

• @utcp/http <= 1.1.1 — vulnerable. Both the loopback-redirect (http://127.0.0.1) and the non-loopback internal-IP variants (e.g. http://169.254.169.254, http://10.0.0.5) succeed. Note: the streamable_http and sse callToolStreaming paths in 1.1.1 are TODO placeholders and don't actually fetch URLs, so the runtime SSRF surface in these protocols is currently confined to discovery — a future implementation must also call ensureSecureUrl before issuing the request.
• @utcp/http 1.1.2 — full fix. Runtime revalidation in callTool closes the non-loopback variants; the OpenApiConverter rejects, at conversion time, any spec fetched from a non-loopback source that declares a loopback servers[0].url, closing the loopback-redirect variant.

Impact

A remote attacker who can convince the agent (via the LLM context, prompt injection, or a tool-discovery surface) to register their HTTPS OpenAPI URL can:

• Map internal networks behind the agent.
• Read AWS/GCP IAM credentials from cloud metadata endpoints (http://169.254.169.254, http://metadata.google.internal).
• Reach unauthenticated internal services exposed on loopback (Elasticsearch, Redis HTTP, internal admin panels, the agent's own HTTP server).
• Have responses returned to the LLM, which combined with prompt injection enables exfiltration back to the attacker.

Patch

Commit on dev: 21f63e6.

New helper packages/http/src/_security.ts exposes isSecureUrl, isLoopbackUrl, ensureSecureUrl. Hostname-based validation closes the prefix bypass (http://localhost.evil.com → rejected). All three protocols' registerManual now call ensureSecureUrl(url, 'manual discovery'); callTool re-checks the resolved URL with ensureSecureUrl(url, 'tool invocation') immediately before the axios request. OpenApiConverter rejects remote spec → loopback server.

Workarounds

For users who cannot upgrade immediately:

• Refuse to call registerManual with any URL controlled by an untrusted party, even over HTTPS.
• Restrict outbound network access from the host running the agent so internal addresses (RFC1918, 169.254.0.0/16, loopback) are unreachable.

Credit

Discovered and reported by @YLChen-007 against the Python sibling implementation (universal-tool-calling-protocol/python-utcp#83). The TypeScript port shared the same code shape and the same vulnerability.