MCP Inspector is Vulnerable to Potential Command Execution via XSS When Connecting to an Untrusted MCP Server

published 2025-09-08 14 mo ago modified 2026-06-17 4 mo ago also GHSA-g9hg-qhmf-q45m , EUVD-2025-27271

cvss: 8.6; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.7%; EPSS 0.7% chance of exploitation in 30 days, percentile 53%
public exploits: 0; none known

The MCP inspector is a developer tool for testing and debugging MCP servers. A cross-site scripting issue was reported in versions of the MCP Inspector local development tool prior to 0.16.6 when connecting to untrusted remote MCP servers with a malicious redirect URI. This could be leveraged to interact directly with the inspector proxy to trigger arbitrary command execution. Users are advised to update to 0.16.6 to resolve this issue.

Patch / fix

fixed in 1 links 1

npm @modelcontextprotocol/inspector 0.16.6

github.com/modelcontextprotocol/inspector@650f309 commit

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: total
Assessed: 14 mo ago (2025-09-09)

Exploit prediction

0.70% chance of exploitation in the next 30 days, higher than 53% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	8.6	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CNA	4.0	8.6	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/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 packages

ecosystem	package	affected	fixed in
npm	@modelcontextprotocol/inspector	<0.16.6	0.16.6

Affected products

modelcontextprotocol inspector

Classification

Weakness

CWE-84 Improper Neutralization of Encoded URI Schemes in a Web Page
CWE-79 Improper Neutralization of Input During Web Page Generation
CWE-94 Improper Control of Generation of Code

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary