6.9

CVE-2026-59951: modelcontextprotocol python-sdk Uncontrolled Resource Consumption

CVSS: 6.9v4.0MediumAwaiting analysis
AliasesGHSA-84m7-p3x7-pcfvCGA-qm45-j5j8-m5cpCGA-rm37-qwx2-fvgf
Published 14-10-2026Last modified 15-10-2026
Open JSON

Vulnerability summary

CVE-2026-59951 is a medium (CVSS 6.9) Uncontrolled Resource Consumption vulnerability in modelcontextprotocol python-sdk. EPSS estimates a 0.46% chance of exploitation in the next 30 days, higher than 38.3% of scored vulnerabilities.

Overall risk
28/100
0100
Medium · default modelHow is this calculated?
CVSS score
6.9/10
010
Medium · v4.0 (CVE.org)
EPSS score
0.46%
0%100%
Low · Change unavailable
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 14-10-2026
    PublishedVulnerability first disclosed.
  2. 15-10-2026
    Last modifiedVulnerability information updated.

Description

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, MCPServer, Server.streamable_http_app(), and StreamableHTTPSessionManager, retain session entries without an idle expiration or aggregate session-count limit. DELETE, refused opening requests, and completed sessions do not reliably discard their entries, and each entry can retain parsed initialize parameters. A client that can reach the endpoint can therefore create ordinary short requests that grow server memory without bound until restart. Stateless HTTP, stdio, and SSE transports are not affected. This issue is fixed in versions 1.30.0 and 2.2.0.

CVSS metrics

6 scores · 5 sources · 2 versions

EPSS trend

Probability

0.46%

Chance of exploitation in the next 30 days

Percentile

38%

Versus all other CVEs

30-day change

Change unavailable

Change unavailable

15-10-202620-10-2026
EPSS score
0.46%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Chainguard5 products
  • nemo-gymAll versions (No fix recorded)
  • nemo-rl-cuda-13.0-gymAll versions (No fix recorded)
  • nemo-rl-cuda-13.0-vllmAll versions (No fix recorded)
  • open-webuiAll versions (No fix recorded) | < 0.12.3-r1
  • semgrepAll versions (No fix recorded) | < 1.181.0-r4
Wolfi2 products
  • open-webuiAll versions (No fix recorded) | < 0.12.3-r1
  • semgrepAll versions (No fix recorded) | < 1.181.0-r4
Modelcontextprotocol1 product
  • python-sdk≥ 1.8.0, < 1.30.0 | ≥ 2.0.0, < 2.2.0
PyPI1 product
  • mcp≥ 1.8.0, < 1.30.0 | ≥ 2.0.0, < 2.2.0

4 vendors · 9 products

References

10 links