CVE-2026-62863

MoLing SSE sessions exposed to malicious web pages

gojue · MoLing MCP computer/browser server

First documented disclosure · Review checkpoint

Summary

A malicious webpage can read a local SSE session identifier and gain access to enabled MCP tools.

Severity and exploitation evidence

Critical · 9.6/10 · CVSS 3.1. Severity source.

Exploitation not established: Controlled research or code-path evidence; the reviewed sources do not establish malicious exploitation or a confirmed victim.

Exploitation evidence source

Technical severity is not a measure of observed attacks or of risk to your deployment. Attempts, demonstrations, and successful compromise retain the qualifications in the source.

How the weakness works

SSE mode lacked authentication and returned wildcard CORS headers, allowing cross-origin EventSource reads of the session endpoint.

Conditions required

The victim runs affected MoLing in SSE mode and visits an attacker-controlled webpage able to reach the listening service; loopback binding alone does not prevent this browser path.

Potential impact

Unauthorized tool calls can reach local files or command execution according to the configured tools and process privileges. The original proof of concept demonstrates session disclosure, not a confirmed victim compromise.

Affected versions and configurations

MoLing through 0.4.0 (CNA: before 0.5.0), when SSE mode is enabled.

Fix and mitigation status

0.5.0 adds authentication, removes wildcard CORS and requires JSON POST content types.

Practical next steps

Upgrade and verify SSE token authentication. Until then disable SSE mode in environments exposed to untrusted browsing; do not rely on loopback binding alone.

Operating lesson

Local agent servers need authentication and browser-origin controls.

Evidence and limits

Original public issue #41 is March 14, fix and release March 15, advisory June 27, CVE October 30. The older advisory’s loopback suggestion is not a complete workaround for its own browser-based scenario.

Sources