CVE-2026-81091: Software Security Vulnerability Vulnerability

HIGH
Advisory Identifier: GHSA-23qx-5wch-w72w
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CVSS 8.6
CWE-918
Published
Advisory Summary

CVE-2026-81091 is a HIGH (CVSS 8.6) security vulnerability vulnerability (CWE-918: Server-Side Request Forgery (SSRF)) affecting Software libraries in the Maven ecosystem. The weakness occurs when the web server receives a url or similar request from an upstream component and retrieves the contents of this url, but it does not sufficiently ensure that the request is being sent to the expected destination.. Remediation is available in the latest vendor maintenance releases.

CVE-2026-81091 at a Glance

CVE Identifier CVE-2026-81091
GHSA Identifier GHSA-23qx-5wch-w72w
Severity HIGH
CVSS v3.1 Base Score 8.6
CWE Classification CWE-918: Server-Side Request Forgery (SSRF)
Affected Product Software
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 8.6

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Changed (S:C)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2026-81091

To remediate this vulnerability, upgrade all affected Software dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-81091, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree

Analyze the terminal output to locate any version of Software in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The mvn dependency:tree command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-918: Server-Side Request Forgery (SSRF), where the web server receives a url or similar request from an upstream component and retrieves the contents of this url, but it does not sufficiently ensure that the request is being sent to the expected destination. In Software, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

References

GitHub Advisory / Wiki ADVISORY
https://github.com/mcp-use/mcp-use/security/advisories/GHSA-f2jg-rm2x-hc5p
NVD — CVE-2026-81091 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-81091
Software Source Repository REPOSITORY
https://github.com/mcp-use/mcp-use
www.vulncheck.com/advisories/mcp-use-... WEB
https://www.vulncheck.com/advisories/mcp-use-inspector-proxy-server-side-request-forgery-via-caller-supplied-target-url

Frequently Asked Questions

What is CVE-2026-81091?
CVE-2026-81091 is a security vulnerability in Software classified as a security vulnerability vulnerability under CWE-918: Server-Side Request Forgery (SSRF).
Which Software versions are affected?
Affected versions include releases prior to current release patches.
What version fixes CVE-2026-81091?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
What is the CVSS score of CVE-2026-81091?
CVE-2026-81091 has a CVSS v3.1 base score of 8.6 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N.
What CWE is associated with CVE-2026-81091?
CVE-2026-81091 is classified under CWE-918: Server-Side Request Forgery (SSRF) (The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.).
How can I check Maven dependencies for CVE-2026-81091?
Run the dependency tree command: 'mvn dependency:tree'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-23qx-5wch-w72w",
  "modified" : "2026-08-27T18:32:25Z",
  "published" : "2026-08-27T18:32:25Z",
  "aliases" : [ "CVE-2026-81091" ],
  "details" : "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" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N"
  }, {
    "type" : "CVSS_V4",
    "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"
  } ],
  "affected" : [ ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-918" ],
    "severity" : "HIGH",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-08-27T17:20:51Z"
  }
}