skoveit/cve-2026-34227Proof-of-concept demonstrating CORS to CSRF chain on Sliver's unauthenticated MCP interface, enabling silent interaction with C2 from any webpage.
Sliver's MCP server spins up an unauthenticated SSE interface and fires back Access-Control-Allow-Origin: * on every response.
The mcp-go library doesn't validate Content-Type, so Simple Requests (text/plain) skip the browser's preflight check entirely. No OPTIONS. No CORS block. No auth. Any page an operator visits can silently talk to their C2.
→ GitHub Security Advisory GHSA-6fpf-248c-m7wm
discovered and reported by @skoveit
