fix: prevent command injection in example URL opening#2082
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| if parsed.scheme.lower() not in ALLOWED_SCHEMES: | ||
| print(f"Refusing to open URL with unsupported scheme '{parsed.scheme}': {url}") |
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should this throw e.g. a ValueError instead of just printing?
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yea moved out of here into the handle elicitation function
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| @@ -124,12 +132,7 @@ def extract_domain(url: str) -> str: | |||
| def open_browser(url: str) -> None: | |||
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Yea not really, will remove.
Replace platform-specific subprocess calls with webbrowser.open() and add URL scheme validation to the elicitation example client. The previous Windows code path used shell=True with subprocess, which allowed command injection via crafted URLs containing shell metacharacters (e.g., & as a command separator in cmd.exe). Changes: - Remove subprocess/sys imports, use webbrowser.open() for all platforms - Add URL scheme allowlist (http/https only) in handle_url_elicitation, validated before prompting the user for consent - Return ElicitResult(action='decline') for disallowed schemes instead of silently continuing with action='accept' - Simplify open_browser() to a pure browser-opening helper - Align with the safe pattern already used in the OAuth example client
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Backport of #2082 to v1.x. Replace platform-specific subprocess calls with webbrowser.open() and add URL scheme validation (http/https allowlist) to block dangerous protocol handlers in the URL elicitation example client.
This was referenced Feb 18, 2026
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Summary
Fix a command injection issue in the URL elicitation example client (
examples/snippets/clients/url_elicitation_client.py).Problem
The
open_browser()function usedsubprocess.run(["start", url], shell=True)on Windows, which allows shell metacharacter injection via crafted URLs. A malicious MCP server could send a URL likehttps://example.com/?state=abc&calcduring URL elicitation, andcmd.exewould interpret&as a command separator, executingcalc(or any arbitrary command).Fix
subprocesscalls withwebbrowser.open(), which handles cross-platform browser opening safely without shell invocationhttp,https) before prompting the user, returningElicitResult(action="decline")for disallowed schemesopen_browser()to a pure browser-opening helpersubprocessandsysimportsThis aligns with the safe pattern already used in
examples/clients/simple-auth-client/mcp_simple_auth_client/main.py.AI Disclaimer