CVE catalog
CVE-2026-59951
The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). From 1.8.0 until 1.30.0 and 2.2.0, stateful Streamable HTTP servers, including FastMCP, MCPServe
- Severity
- High · CVSS 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Published
- Updated
- Source
- [NVD] · [CVE record]
- EPSS
- 0.46% · Oct 27, 2026
A flaw was found in the Model Context Protocol (MCP) Python SDK. Stateful streamable HTTP servers fail to enforce idle session expiration or limits on active sessions, preventing terminated or rejected requests from releasing their resources. A remote attacker can exploit this issue by repeatedly sending requests to accumulate unreleased session entries in memory, ultimately causing a Denial of Service (DoS) due to memory exhaustion. mcp: mcp: Denial of Service via session memory exhaustion in streamable HTTP servers The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.
Vulnerable and fixed packages
Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.
| Distribution | Package | Release | Version | Status |
|---|---|---|---|---|
| PyPI | mcp | Not reported | 2.0.0 | vulnerable |
| PyPI | mcp | Not reported | 2.0.1 | vulnerable |
| PyPI | mcp | Not reported | 2.1.0 | vulnerable |
| PyPI | mcp | Not reported | 2.1.1 | vulnerable |
| PyPI | mcp | Not reported | 2.2.0 | fixed |
Fixed-version evidence
| Distribution | Package | Type | Release | Fixed version | Urgency | Origin | Bugs |
|---|---|---|---|---|---|---|---|
| PyPI | mcp | PyPI | Not reported | 2.2.0 | Not reported | GHSA-84M7-P3X7-PCFV | Not reported |
OpenFactory catalog packages
No matching packages in this catalog.
Observed:
References
- [https://github.com/advisories/GHSA-84m7-p3x7-pcfv]
- [https://nvd.nist.gov/vuln/detail/CVE-2026-59951]
- [https://osv.dev/vulnerability/GHSA-84m7-p3x7-pcfv]
- [https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-59951.json]
[FIRST EPSS] · [GitHub Advisory Database] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX]