GHSA-39J6-4867-GG4W
Vulnerability from github – Published: 2026-05-07 22:32 – Updated: 2026-05-15 23:45Summary
The utcp-http plugin is vulnerable to a blind Server-Side Request Forgery (SSRF) caused by a trust-boundary inconsistency between manual discovery and tool invocation. register_manual() validates the discovery URL against an HTTPS / loopback allowlist, but call_tool() and call_tool_streaming() reuse the resolved tool_call_template.url directly without revalidating. An attacker who hosts a malicious OpenAPI spec on a legitimate HTTPS endpoint can declare servers: [{ url: "http://169.254.169.254" }] (or any internal address) in the spec; the OpenAPI converter blindly trusts that value and the tool becomes a blind SSRF primitive that exposes cloud metadata, internal services, and other firewalled-only endpoints to the LLM caller.
All three HTTP-class protocols (utcp_http.http, utcp_http.streamable_http, utcp_http.sse) shared the same gap, plus a separate prefix-bypass: the previous startswith("http://localhost") check let URLs like http://localhost.evil.com through.
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 (Elasticsearch, Redis HTTP, internal admin panels).
- Have responses returned to the LLM, which combined with prompt injection enables exfiltration back to the attacker.
Affected versions
utcp-http <= 1.1.1.
Patched versions
utcp-http 1.1.2.
Patch
Commit: 5b16e43 on dev.
- New
utcp_http._securityhelper:ensure_secure_url(url, context=...)parses the URL withurllib.parse.urlparseand validates the hostname (not a string prefix) against the loopback set, closing thelocalhost.evil.combypass. - All three protocols call
ensure_secure_url(url, context="manual discovery")inregister_manual(replacing the duplicated prefix check) andensure_secure_url(url, context="tool invocation")immediately before each aiohttp request incall_tool/call_tool_streaming. The runtime check is the actual SSRF fix. - New regression tests in
test_security.pypin the accept/reject decisions and explicitly cover the historical bypass cases.
Workarounds
For users who cannot upgrade immediately:
- Refuse to call register_manual 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 for cloud metadata) are unreachable.
Credit
Discovered and reported by @YLChen-007 in #83.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 1.1.1"
},
"package": {
"ecosystem": "PyPI",
"name": "utcp-http"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.1.2"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-44661"
],
"database_specific": {
"cwe_ids": [
"CWE-918"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-07T22:32:54Z",
"nvd_published_at": "2026-05-14T21:16:47Z",
"severity": "MODERATE"
},
"details": "## Summary\n\nThe `utcp-http` plugin is vulnerable to a blind Server-Side Request Forgery (SSRF) caused by a trust-boundary inconsistency between manual discovery and tool invocation. `register_manual()` validates the discovery URL against an HTTPS / loopback allowlist, but `call_tool()` and `call_tool_streaming()` reuse the resolved `tool_call_template.url` directly without revalidating. An attacker who hosts a malicious OpenAPI spec on a legitimate HTTPS endpoint can declare `servers: [{ url: \"http://169.254.169.254\" }]` (or any internal address) in the spec; the OpenAPI converter blindly trusts that value and the tool becomes a blind SSRF primitive that exposes cloud metadata, internal services, and other firewalled-only endpoints to the LLM caller.\n\nAll three HTTP-class protocols (`utcp_http.http`, `utcp_http.streamable_http`, `utcp_http.sse`) shared the same gap, plus a separate prefix-bypass: the previous `startswith(\"http://localhost\")` check let URLs like `http://localhost.evil.com` through.\n\n## Impact\n\nA 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:\n- Map internal networks behind the agent.\n- Read AWS/GCP IAM credentials from cloud metadata endpoints (`http://169.254.169.254`, `http://metadata.google.internal`).\n- Reach unauthenticated internal services (Elasticsearch, Redis HTTP, internal admin panels).\n- Have responses returned to the LLM, which combined with prompt injection enables exfiltration back to the attacker.\n\n## Affected versions\n\n`utcp-http \u003c= 1.1.1`.\n\n## Patched versions\n\n`utcp-http 1.1.2`.\n\n## Patch\n\nCommit: 5b16e43 on `dev`.\n\n- New `utcp_http._security` helper: `ensure_secure_url(url, context=...)` parses the URL with `urllib.parse.urlparse` and validates the hostname (not a string prefix) against the loopback set, closing the `localhost.evil.com` bypass.\n- All three protocols call `ensure_secure_url(url, context=\"manual discovery\")` in `register_manual` (replacing the duplicated prefix check) and `ensure_secure_url(url, context=\"tool invocation\")` immediately before each aiohttp request in `call_tool` / `call_tool_streaming`. The runtime check is the actual SSRF fix.\n- New regression tests in `test_security.py` pin the accept/reject decisions and explicitly cover the historical bypass cases.\n\n## Workarounds\n\nFor users who cannot upgrade immediately:\n- Refuse to call `register_manual` with any URL controlled by an untrusted party, even over HTTPS.\n- Restrict outbound network access from the host running the agent so internal addresses (RFC1918, 169.254.0.0/16, loopback for cloud metadata) are unreachable.\n\n## Credit\n\nDiscovered and reported by [@YLChen-007](https://github.com/YLChen-007) in #83.",
"id": "GHSA-39j6-4867-gg4w",
"modified": "2026-05-15T23:45:57Z",
"published": "2026-05-07T22:32:54Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/universal-tool-calling-protocol/python-utcp/security/advisories/GHSA-39j6-4867-gg4w"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44661"
},
{
"type": "PACKAGE",
"url": "https://github.com/universal-tool-calling-protocol/python-utcp"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "utcp-http vulnerable to SSRF via attacker-controlled OpenAPI servers[0].url in HTTP communication protocol"
}
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