Vulnerability-Lookup

CVE-2026-81091 (GCVE-0-2026-81091)

Vulnerability from cvelistv5 – Published: 2026-08-27 14:50 – Updated: 2026-08-29 11:48

Title

mcp-use Inspector Proxy Server-Side Request Forgery via Caller-Supplied Target URL

Summary

The proxy middleware in mcp-use's inspector forwards requests to a destination the caller names. mountMcpProxy in libraries/typescript/packages/inspector/src/server/proxy/mcp-proxy.ts read the target from the X-Target-URL header or the __mcp_target parameter and proxied to it without inspecting the host, so loopback, link-local and private addresses were all accepted, as were names that resolve to them, and the validation was not reapplied to a redirect the destination returned. A caller could therefore make the server issue requests to addresses reachable only from the host it runs on and read the responses. The current code calls isSafeProxyTarget, which checks the resolved address against private, loopback and link-local ranges before proxying and bounds the number of redirects followed.

Severity

8.7 (High)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

8.6 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-27 18:12 UTC

CWE

CWE-918 - Server-Side Request Forgery (SSRF)

Assigner

VulnCheck mitre root

References

3 references

URL	Tags
https://github.com/mcp-use/mcp-use	product
https://github.com/mcp-use/mcp-use/security/advis…	vendor-advisory
https://www.vulncheck.com/advisories/mcp-use-insp…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version	CPE status
mcp-use	mcp-use	Affected: 0 , ≤ 2.3.2 (semver)	guessed

Date Public

2026-08-26 00:00

Credits

Yotam Perkal (Pluto Security)

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-81091

Vulnerability from fkie_nvd - Published: 2026-08-27 17:20 - Updated: 2026-08-27 20:18

Severity

8.6 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Summary

References

	URL	Tags
	disclosure@vulncheck.com	https://github.com/mcp-use/mcp-use
	disclosure@vulncheck.com	https://github.com/mcp-use/mcp-use/security/advisories/GHSA-f2jg-rm2x-hc5p
	disclosure@vulncheck.com	https://www.vulncheck.com/advisories/mcp-use-inspector-proxy-server-side-request-forgery-via-caller-supplied-target-url

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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  "lastModified": "2026-08-27T20:18:49.180",
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    {
      "source": "disclosure@vulncheck.com",
      "url": "https://github.com/mcp-use/mcp-use/security/advisories/GHSA-f2jg-rm2x-hc5p"
    },
    {
      "source": "disclosure@vulncheck.com",
      "url": "https://www.vulncheck.com/advisories/mcp-use-inspector-proxy-server-side-request-forgery-via-caller-supplied-target-url"
    }
  ],
  "sourceIdentifier": "disclosure@vulncheck.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-918"
        }
      ],
      "source": "disclosure@vulncheck.com",
      "type": "Secondary"
    }
  ]
}

GHSA-23QX-5WCH-W72W

Vulnerability from github – Published: 2026-08-27 18:32 – Updated: 2026-08-27 18:32

Details

Severity

8.6 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

8.7 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Show details on source website

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{
  "affected": [],
  "aliases": [
    "CVE-2026-81091"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-918"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-27T17:20:51Z",
    "severity": "HIGH"
  },
  "details": "The proxy middleware in mcp-use\u0027s inspector forwards requests to a destination the caller names. mountMcpProxy in libraries/typescript/packages/inspector/src/server/proxy/mcp-proxy.ts read the target from the X-Target-URL header or the __mcp_target parameter and proxied to it without inspecting the host, so loopback, link-local and private addresses were all accepted, as were names that resolve to them, and the validation was not reapplied to a redirect the destination returned. A caller could therefore make the server issue requests to addresses reachable only from the host it runs on and read the responses. The current code calls isSafeProxyTarget, which checks the resolved address against private, loopback and link-local ranges before proxying and bounds the number of redirects followed.",
  "id": "GHSA-23qx-5wch-w72w",
  "modified": "2026-08-27T18:32:25Z",
  "published": "2026-08-27T18:32:25Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mcp-use/mcp-use/security/advisories/GHSA-f2jg-rm2x-hc5p"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-81091"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mcp-use/mcp-use"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/mcp-use-inspector-proxy-server-side-request-forgery-via-caller-supplied-target-url"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-81091 (GCVE-0-2026-81091)

FKIE_CVE-2026-81091

GHSA-23QX-5WCH-W72W

Tags

Sightings

Nomenclature