CVE-2026-101057

utcp-mcp before 1.1.3 SSRF via unvalidated MCP server URL

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Published Sep 27, 2026 CVSS 4.0 · 2.3 Low EPSS < 1% KEV · Not listed
Description
utcp-mcp (the MCP plugin of python-utcp) through 1.1.2 connects to the HTTP and WebSocket MCP server URLs given in a call template's mcpServers configuration without the ensure_secure_url validation that the HTTP-family plugins apply, so the HTTPS/WSS-or-loopback rule is not enforced. A call template naming a plain-HTTP, non-loopback MCP server URL is dialed as configured, exposing the MCP handshake to network interception and permitting cleartext connections to internal hosts. The mcpServers configuration is operator-authored rather than remote data, and the connection is an MCP handshake rather than an arbitrary request returning a body, which limits practical exploitation; the OAuth2 token_url credential path described in the original report was not reachable in the affected versions, because the OAuth2 handler was never invoked and the call template's auth field was not read. Fixed in utcp-mcp 1.1.3, which validates server URLs before any connection is made.

Analysis

AI-generated

Technical impact

The utcp-mcp plugin (versions prior to 1.1.3) accepts any HTTP or WebSocket server URLs specified in the mcpServers section of an operator‑authored call template. Because the plugin does not enforce HTTPS, WSS, or loopback restrictions, it can initiate cleartext connections to internally reachable MCP servers. This exposes the MCP handshake traffic, which contains authentication tokens and internal host identifiers, to interception. The vulnerability is a form of Cleartext Transmission of Sensitive Information (CWE‑319) and does not allow arbitrary network requests; its usefulness is limited to observing the handshake rather than executing arbitrary code.

Affected Systems

All installations of universal‑tool‑calling‑protocol:python‑utcp that use the utcp‑mcp plugin before version 1.1.3 are affected. The risk materializes when a call template contains a plain‑HTTP or non‑loopback URL in the mcpServers configuration. Because call templates are authored by operators, the vulnerability is only exploitable where such templates exist.

Risk and Exploitability

With a CVSS score of 2.3, the vulnerability is classified as low severity and no EPSS data is available. It is not listed in CISA's KEV catalog. The likely attack vector is an internal operator modifying or supplying a call template that references a non‑HTTPS MCP server, as inferred from the fact that the configuration is operator‑authored. Exploitation requires this modification and is not remotely achievable from an external attacker. The impact is the interception of cleartext MCP handshake data and potential internal host enumeration, rather than arbitrary data exfiltration. Overall, the risk is low to moderate.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Update utcp‑mcp to version 1.1.3 or later to enforce URL validation before connection is established.
  • Remove any plain‑HTTP or non‑loopback MCP server URLs from operator‑authored call templates and ensure HTTPS is used.
  • Audit existing call templates for unvalidated URLs and correct any that remain.
  • Optionally, monitor network traffic for unexpected cleartext MCP handshakes and block plain‑HTTP connections if the internal policy requires it.

Generated by OpenCVE AI on September 27, 2026 at 19:22 UTC.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}
Type Values Removed Values Added
First Time appeared Universal-tool-calling-protocol
Universal-tool-calling-protocol python-utcp
Vendors & Products Universal-tool-calling-protocol
Universal-tool-calling-protocol python-utcp
Type Values Removed Values Added
Description utcp-mcp (the MCP plugin of python-utcp) through 1.1.2 connects to the HTTP and WebSocket MCP server URLs given in a call template's mcpServers configuration without the ensure_secure_url validation that the HTTP-family plugins apply, so the HTTPS/WSS-or-loopback rule is not enforced. A call template naming a plain-HTTP, non-loopback MCP server URL is dialed as configured, exposing the MCP handshake to network interception and permitting cleartext connections to internal hosts. The mcpServers configuration is operator-authored rather than remote data, and the connection is an MCP handshake rather than an arbitrary request returning a body, which limits practical exploitation; the OAuth2 token_url credential path described in the original report was not reachable in the affected versions, because the OAuth2 handler was never invoked and the call template's auth field was not read. Fixed in utcp-mcp 1.1.3, which validates server URLs before any connection is made.
Title utcp-mcp before 1.1.3 SSRF via unvalidated MCP server URL
Weaknesses CWE-319
References
Metrics cvssV3_1

{'score': 3.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N'}

cvssV4_0

{'score': 2.3, 'vector': 'CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N'}
Weaknesses
  • CWE-319

    Cleartext Transmission of Sensitive Information

Sources

Status
PUBLISHED
Assigner
VulnCheck
Published
Updated
Sep 30, 2026, 3:38 PM
Reserved
Sep 27, 2026, 4:38 PM

View source JSON

Updated
Sep 30, 2026, 3:38 PM

JSON

Status
Deferred
Published
Sep 27, 2026, 6:16 PM
Modified
Sep 30, 2026, 5:32 PM

View source JSON

No data.

Updated
Sep 27, 2026, 7:45 PM

JSON