CVE-2026-52870: MCP Python SDK: Experimental task handlers allow any client to access and cancel other clients' tasks
In affected versions, the default request handlers installed by the experimental tasks feature (server.experimental.enable_tasks()) did not check which session created a task before acting on it. On a server with more than one connected client, any client could observe, read results from, and cancel tasks belonging to other clients.
References
- github.com/advisories/GHSA-hvrp-rf83-w775
- github.com/modelcontextprotocol/python-sdk/commit/62137874ff26dd74d2fea80ff528a7fd9ca7a5e7
- github.com/modelcontextprotocol/python-sdk/pull/2720
- github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2
- github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-hvrp-rf83-w775
- nvd.nist.gov/vuln/detail/CVE-2026-52870
Code Behaviors & Features
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