appium-mcp: Unescaped Locator Data XSS in MCP-UI Resource (createLocatorGeneratorUI)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-58500: 0.40% estimated exploitation activity in the next 30 days; percentile 34.33 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Unescaped Locator Data XSS in MCP-UI Resource (createLocatorGeneratorUI) Summary appium-mcp's createLocatorGeneratorUI function interpolates attacker-controlled element attributes — text, content-desc, resource-id, and locator selector values — directly into an HTML template literal without any HTML or JavaScript context escaping. An attacker who controls the UI of the app under test can inject arbitrary HTML and JavaScript into the MCP UI resource returned by the generatelocators tool. When a victim's MCP client renders this resource, the injected script executes and can invoke arbitrary MCP tools via window.parent.postMessage, leading to unauthorized MCP tool execution such as taking screenshots, reading page source, or any other registered capability. Details The vulnerability is a stored/reflected cross-site scripting (XSS) issue in the MCP UI generation pipeline. Vulnerable sink — src/ui/mcp-ui-utils.ts:730–740: None of element.text, element.contentDesc, element.resourceId,…

Published by the source

19 Jun 2026, 21:43 UTC

Last modified by the source

15 Jul 2026, 02:26 UTC

Source last checked

26 Oct 2026, 12:56 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-x975-rgx4-5fh4

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-x975-rgx4-5fh4

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# Patch Next advisory brief: CVE-2026-58500

Advisory: appium-mcp: Unescaped Locator Data XSS in MCP-UI Resource (createLocatorGeneratorUI)
IDs: CVE-2026-58500, GHSA-x975-rgx4-5fh4
Record: https://patchnext.com/advisories/cve-2026-58500 (revision 2, source checked 26 Oct 2026, 12:56 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: appium-mcp 1.85.10. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm appium-mcp: affected <= 1.85.9; fixed in 1.85.10

## Suggested inspection (read-only)
- `npm ls appium-mcp --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on appium-mcp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-x975-rgx4-5fh4 (OSV record GHSA-x975-rgx4-5fh4 lists affected ranges: npm appium-mcp >=0 <1.85.10 (fixed))
- Verified: https://github.com/advisories/GHSA-x975-rgx4-5fh4 (GitHub-reviewed advisory GHSA-x975-rgx4-5fh4 lists affected ranges: npm appium-mcp >=0 <=1.85.9)

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