CVE-2025-53365: Model Context Protocol Python SDK denial of service in HTTP transport

Executive brief

The Model Context Protocol (MCP) Python SDK contains a flaw that allows a remote user to crash the server. By establishing a specific type of web connection and then triggering an error, an attacker can force the server to shut down unexpectedly. This results in a denial of service, requiring a manual restart to restore operations.

Technical details

An unhandled exception vulnerability (CWE-248) exists in the MCP Python SDK's streamable HTTP transport component. If a client establishes a streamable HTTP session and subsequently triggers an exception, the server fails to catch a 'ClosedResourceError'. This uncaught exception leads to a process crash. The attack can be carried out over the network without prior authentication or user interaction. A fix is available in version 1.10.0, which implements proper exception handling for these transport sessions.

Affected products

• Model Context Protocol mcp < 1.10.0

Timeline

• 2025-07-04: disclosed
• 2025-07-04: advisory
• 2025-07-04: patched: Version 1.10.0 released

References

• https://api.github.com/users/rharang
• https://github.com/rharang
• https://api.github.com/users/rharang/gists%7B/gist_id%7D
• https://api.github.com/users/rharang/repos
• https://avatars.githubusercontent.com/u/8082617?v=4
• https://api.github.com/users/rharang/events%7B/privacy%7D