CVE-2026-32112: CVE-2026-32112: Cross-Site Scripting in Home Assistant MCP Server OAuth Flow

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CVE-2026-32112: Cross-Site Scripting in Home Assistant MCP Server OAuth Flow

Vulnerability ID: CVE-2026-32112
CVSS Score: 6.8
Published: 2026-03-12

The Home Assistant MCP Server (ha-mcp) prior to version 7.0.0 contains a Cross-Site Scripting (XSS) vulnerability within its beta OAuth consent form. The application dynamically constructs HTML using Python f-strings without proper input sanitization, allowing attackers to execute arbitrary JavaScript in the context of the server operator's browser session.

TL;DR

ha-mcp versions before 7.0.0 are vulnerable to Stored and Reflected XSS in the beta ha-mcp-oauth mode. Attackers can steal Home Assistant tokens by tricking operators into clicking crafted authorization links.

⚠️ Exploit Status: POC

Technical Details

CWE ID: CWE-79
Attack Vector: Network
CVSS Base Score: 6.8
EPSS Score: 0.00033
Exploit Status: Proof of Concept
KEV Status: Not Listed

Affected Systems

ha-mcp (Home Assistant MCP Server)
ha-mcp-oauth beta mode
ha-mcp: < 7.0.0 (Fixed in: 7.0.0)

Code Analysis

Commit: 3b93c4d

Dependency Update: Update fastmcp to 3.1.0 to enforce strict output encoding

Mitigation Strategies

Upgrade ha-mcp to version 7.0.0 or later
Disable the beta ha-mcp-oauth mode
Implement a restrictive Content Security Policy (CSP)
Restrict network access to the ha-mcp endpoints

Remediation Steps:

Log in to the system hosting the ha-mcp server.
Update the ha-mcp package to version 7.0.0 or higher.
If immediate updating is impossible, alter the configuration to disable the ha-mcp-oauth beta feature.
Restart the ha-mcp service to apply the updated dependencies or configuration.
Audit connected clients and Home Assistant access logs for unauthorized token usage or API requests.

References

Read the full report for CVE-2026-32112 on our website for more details including interactive diagrams and full exploit analysis.

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