8.7

CVE-2025-53366: modelcontextprotocol python-sdk Uncaught Exception

CVSS: 8.7v4.0HighDeferred
AliasesGHSA-3qhf-m339-9g5vPYSEC-2026-1616
Published 04-07-2025Last modified 08-07-2025
Open JSON

Vulnerability summary

CVE-2025-53366 is a high (CVSS 8.7) Uncaught Exception vulnerability in modelcontextprotocol python-sdk. EPSS estimates a 9.31% chance of exploitation in the next 30 days, higher than 95.3% of scored vulnerabilities.

Overall risk
37/100
0100
Medium · default modelHow is this calculated?
CVSS score
8.7/10
010
High · v4.0 (CVE.org)
EPSS score
9.31%
0%100%
Low · +2.05 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 04-07-2025
    PublishedVulnerability first disclosed.
  2. 08-07-2025
    Last modifiedVulnerability information updated.

Description

The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to version 1.9.4, a validation error in the MCP SDK can cause an unhandled exception when processing malformed requests, resulting in service unavailability (500 errors) until manually restarted. Impact may vary depending on the deployment conditions, and presence of infrastructure-level resilience measures. Version 1.9.4 contains a patch for the issue.

CVSS metrics

3 scores · 3 sources · 1 version

EPSS trend

Probability

9.31%

Chance of exploitation in the next 30 days

Percentile

95%

Versus all other CVEs

30-day change

+2.05 pp

From 7.26% on 19-09-2026

19-09-202619-10-2026
EPSS score
9.31%

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

Modelcontextprotocol1 product
PyPI1 product
  • mcp< 1.9.4

2 vendors · 2 products

References

9 links