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.
References
YLChen-007 Reporter
Summary
The
@utcp/httppackage 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, butcallTool()reuses the resolvedtoolCallTemplate.urldirectly without revalidating, and theOpenApiConverterblindly trusts whateverservers[0].urlan 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" }]orservers: [{ 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 likehttp://localhost.evil.comthrough.Sister advisory
This is the npm/TypeScript counterpart of GHSA-39j6-4867-gg4w / CVE-2026-44661 on the Python
utcp-httppackage. 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: thestreamable_httpandssecallToolStreamingpaths 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 callensureSecureUrlbefore issuing the request.@utcp/http 1.1.2— full fix. Runtime revalidation incallToolcloses the non-loopback variants; theOpenApiConverterrejects, at conversion time, any spec fetched from a non-loopback source that declares a loopbackservers[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:
http://169.254.169.254,http://metadata.google.internal).Patch
Commit on
dev: 21f63e6.New helper
packages/http/src/_security.tsexposesisSecureUrl,isLoopbackUrl,ensureSecureUrl. Hostname-based validation closes the prefix bypass (http://localhost.evil.com→ rejected). All three protocols'registerManualnow callensureSecureUrl(url, 'manual discovery');callToolre-checks the resolved URL withensureSecureUrl(url, 'tool invocation')immediately before the axios request.OpenApiConverterrejects remote spec → loopback server.Workarounds
For users who cannot upgrade immediately:
registerManualwith any URL controlled by an untrusted party, even over HTTPS.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.
References