CVE-2025-53365 MCP Python SDK has Unhandled Exception in Streamable HTTP Transport ,Leading to Denial of Service
A malicious client can crash the MCP Python SDK server by triggering an unhandled exception, requiring a restart to restore service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-53365?
CVE-2025-53365 is a high-severity denial of service vulnerability in modelcontextprotocol python-sdk, published on 4 Jul 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to version 1.10.0, if a client deliberately triggers an exception after establishing a streamable HTTP session, this can lead to an uncaught ClosedResourceError on the server side, causing the server to crash and requiring a restart to restore service. Impact may vary depending on the deployment conditions, and presence of infrastructure-level resilience measures. Version 1.10.0 contains a patch for the issue.
Weakness: CWE-248
Which versions are affected by CVE-2025-53365?
3 open source packages ship an affected version, including mcp.
| Package | Affected | Fixed in |
|---|---|---|
mcp PyPI | All versions | 1.10.0 |
mcp PyPI | All versions | 1.10.0 |
mcp PyPI | All versions | 1.10.0 |
How do I fix CVE-2025-53365?
Upgrade mcp to 1.10.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-53365 being exploited?
There is no known exploitation of CVE-2025-53365 in the wild and no public exploit code.
Sources
Also known as GHSA-j975-95f5-7wqh, PYSEC-2026-1618, ROOT-APP-PYPI-CVE-2025-53365.