# MCP Python SDK has Unhandled Exception in Streamable HTTP Transport, Leading to Denial of Service

Advisory record · `GHSA-j975-95f5-7wqh`

- **Identifiers:** `GHSA-j975-95f5-7wqh` · `CVE-2025-53365` · `PYSEC-2026-1618`
- **State:** Confirmed
- **Severity:** CVSS 8.7 High
- **Critical:** No
- **Weakness (CWE):** [CWE-248](https://cwe.mitre.org/data/definitions/248.html)
- **Tags:** [CWE-248](https://agentprime.io/advisories/tag/cwe-248.md)
- **Published:** 4 Jul 2025
- **Updated:** 16 Jul 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 4 Jul 2025, 22:06 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `mcp` (PyPI): affected `<1.10.0`; fixed in `1.10.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> The mcp Python SDK, versions before 1.10.0, is vulnerable to a denial of service in its streamable HTTP transport. A client that deliberately triggers an exception after establishing a streamable HTTP session can cause an uncaught error that crashes the server, which then needs a restart to restore service. Upgrade mcp to version 1.10.0 or later; the source gives few details on deployment-specific impact.

Written 5 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 8.7 High, CVSS 4.0: `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0042, the 36th percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:42 UTC: First seen by agentprime
- 31 Oct 2026, 14:42 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-j975-95f5-7wqh)

## Sources

- [GitHub Advisory Database: GHSA-j975-95f5-7wqh](https://github.com/advisories/GHSA-j975-95f5-7wqh)
- [OSV: GHSA-j975-95f5-7wqh](https://osv.dev/vulnerability/GHSA-j975-95f5-7wqh)
- <https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-j975-95f5-7wqh>
- <https://nvd.nist.gov/vuln/detail/CVE-2025-53365>
- <https://github.com/modelcontextprotocol/python-sdk/pull/967>
- <https://github.com/modelcontextprotocol/python-sdk/commit/7b420656de48cfdb90b39eb582e60b6d55c2f891>
- <https://github.com/advisories/GHSA-j975-95f5-7wqh>
- <https://github.com/modelcontextprotocol/python-sdk>
- <https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.10.0>
- <https://github.com/pypa/advisory-database/tree/main/vulns/mcp/PYSEC-2026-1618.yaml>
- <https://pypi.org/project/mcp>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-j975-95f5-7wqh>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-j975-95f5-7wqh/>. Everything for agents: <https://agentprime.io/llms.txt>.