fix: prevent credential_process hang on Windows in stdio transport mode#293
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rshevchuk-git wants to merge 1 commit into
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fix: prevent credential_process hang on Windows in stdio transport mode#293rshevchuk-git wants to merge 1 commit into
rshevchuk-git wants to merge 1 commit into
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Monkey-patch botocore's ProcessProvider to pass stdin=subprocess.DEVNULL when spawning credential_process subprocesses. Without this, the child inherits the MCP JSON-RPC pipe as stdin, causing Popen.communicate() to hang indefinitely on Windows (IOCP) due to the open pipe handle. Fixes D454977820
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| import httpx | ||
| import json | ||
| import logging | ||
| import subprocess |
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False positive. We dont pass user-controlled input to subprocess, and we use compat_shell_split() (no shell=True). Literally replicating what botocore itself already does, just adding stdin=subprocess.DEVNULL
anasstahr
approved these changes
May 27, 2026
arnewouters
reviewed
May 27, 2026
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| def _retrieve_credentials_using(self, credential_process): | ||
| process_list = compat_shell_split(credential_process) | ||
| p = self._popen( |
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Would the patch be simpler if we just override self._popen with a patched popen that has stdin=subprocess.DEVNULL by default?
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Summary
ProcessProvider._retrieve_credentials_usingto passstdin=subprocess.DEVNULLwhen spawningcredential_processsubprocessesPopen.communicate()to hang indefinitely on Windows (IOCP)Problem
When
mcp-proxy-for-awsruns in stdio transport mode, its stdin is the MCP JSON-RPC pipe. Botocore'sProcessProviderspawnscredential_processsubprocesses without specifyingstdin, so the child inherits the pipe. On Windows this causes the subprocess to hang indefinitely because it holds an open handle to the pipe, blockingPopen.communicate()from completing.This affects any user with
credential_processin their AWS profile (e.g.,isengardcli credentials) when using the MCP proxy on Windows through IDE integrations (Kiro, Cline, Claude Code).Fixes D454977820
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