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Python: Bug: MCPStreamableHttpPlugin.__aenter__() method doesn't treat HTTP 401/403 as fatal errors #13414
Description
Describe the bug
The semantic_kernel MCPStreamableHttpPlugin.aenter() method has a bug - it doesn't treat HTTP 401/403 as fatal errors. It just logs them and keeps waiting.
I think the bug is in the _inner_connect() method of the semantic kernel mcp.py file you shared above.
Python
async def _inner_connect(self, ready_event: asyncio.Event) -> None:
try:
await session.initialize()
except Exception as ex:
await self._exit_stack.aclose()
raise KernelPluginInvalidConfigurationError(
"Failed to initialize session. Please check your configuration."
) from ex
The Bug:
- connect() creates a background task running _inner_connect() and waits for ready_event
- _inner_connect() calls session.initialize(), which makes the HTTP request to the MCP server
- MCP server returns HTTP 401 Unauthorized
- session.initialize() raises an exception
- The exception handler in _inner_connect() raises KernelPluginInvalidConfigurationError
- BUG: The exception handler does NOT call ready_event.set()
- Meanwhile, connect() is still waiting at await ready_event.wait()
- Since ready_event is never set, connect() hangs forever (until PromptFlow's 30-second timeout)
- The exception is trapped in the background task and never propagates to our code
To Reproduce
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- See error
Expected behavior
A clear and concise description of what you expected to happen.
Screenshots
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Platform
- Language: [e.g. C#, Python]
- Source: [e.g. NuGet package version 0.1.0, pip package version 0.1.0, main branch of repository]
- AI model: [e.g. OpenAI:GPT-4o-mini(2024-07-18)]
- IDE: [e.g. Visual Studio, VS Code]
- OS: [e.g. Windows, Mac]
Additional context
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Activity
[-]Bug: MCPStreamableHttpPlugin.__aenter__() method doesn't treat HTTP 401/403 as fatal errors[/-][+].Net: Bug: MCPStreamableHttpPlugin.__aenter__() method doesn't treat HTTP 401/403 as fatal errors[/+][-].Net: Bug: MCPStreamableHttpPlugin.__aenter__() method doesn't treat HTTP 401/403 as fatal errors[/-][+]Python: Bug: MCPStreamableHttpPlugin.__aenter__() method doesn't treat HTTP 401/403 as fatal errors[/+]aryanyk commentedon Jan 3, 2026
Hi Swati Bararia (@bararia-swati) , Evan Mattson (@moonbox3)
I would like to work on this. I can implement the status code check in aenter to raise an explicit exception for 401/403 errors.
VedantMadane commentedon Jan 17, 2026
I'm taking this issue and have a local fix in progress to treat HTTP 401/403 as fatal in MCPStreamableHttpPlugin.aenter with accompanying tests. I'll open a PR shortly.
fix(python): ensure ready_event is set on MCP connection failures
razashariff commentedon Mar 16, 2026
Silently continuing on 401/403 is a fail-open pattern that masks authentication failures. MCPS (MCP Secure) takes the opposite approach — fail-closed by design. The
secureMCP()middleware rejects any message without a valid ECDSA P-256 signature. No valid signature = no processing, no silent fallback.MCPS also provides a layer independent of HTTP status codes — per-message signing means authentication is verified at the message level, not the transport level. Even if the HTTP layer returns 200, a tampered or unsigned message body is rejected.
Published as an IETF Internet-Draft and available on npm as
mcp-secure(zero dependencies).github-actions commentedon Oct 2, 2026
This issue is stale because it has been open for 90 days with no activity.
github-actions commentedon Oct 17, 2026
This issue was closed because it has been inactive for 14 days since being marked as stale.
Python: Propagate MCP initialization failures (microsoft#14095)