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Response snapshot Oct 27, 2026, 01:11 UTC

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VulnerabilityCVE-2026-109527

The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients.

The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. In mcp versions before 1.29.1 and from 2.0.0a1 through 2.0.

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
0.7% in the next 30 days
Sources
1 source

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-109527 (opens a new tab)

What happened

The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. In mcp versions before 1.29.1 and from 2.0.0a1 through 2.0.1, the Streamable HTTP session manager, SSE message endpoint, and OAuth authorization-server routes buffer complete HTTP request bodies without enforcing a maximum size.

An unauthenticated remote client able to reach an affected endpoint can send a large declared or streamed request body that consumes multiple times the body size in process memory and can repeatedly exhaust memory or terminate the server.

Stdio-only servers and deployments with an effective upstream request-size limit are not affected, and applications that use StreamableHTTPServerTransport directly remain responsible for enforcing their own limit. The standard SDK server applications and session managers are fixed in versions 1.29.1 and 2.1.0.

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.7%

Scored Percentile 52.9%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    NVD CVE-2026-109527 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-109527, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 20). The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. (CVE-2026-109527). https://kevwire.com/record/CVE-2026-109527

MLA

"The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. (CVE-2026-109527)." KEVWire, 20 Oct. 2026, kevwire.com/record/CVE-2026-109527.

Chicago

KEVWire. "The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. (CVE-2026-109527)." Last modified October 20, 2026. https://kevwire.com/record/CVE-2026-109527.

Evidence summary (plain text)

The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. (Oct 14, 2026).
The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. In mcp versions before 1.29.1 and from 2.0.0a1 through 2.0.1, the Streamable HTTP session manager, SSE message endpoint, and OAuth authorization-server routes buffer complete HTTP request bodies without enforcing a maximum size. An unauthenticated remote client able to reach an affected endpoint can send a large declared or streamed request body that consumes multiple times the body size in process memory and can repeatedly exhaust memory or terminate the server. Stdio-only servers and deployments with an effective upstream request-size limit are not affected, and applications that use StreamableHTTPServerTransport directly remain responsible for enforcing their own limit. The standard SDK server applications and session managers are fixed in versions 1.29.1 and 2.1.0.
CVSS 7.5 (version 3.1; evidence as of Oct 20, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-109527).
EPSS 0.7% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-109527&date=2026-10-26).
Sources:
NVD CVE-2026-109527: https://nvd.nist.gov/vuln/detail/CVE-2026-109527
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=3000
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-109527&date=2026-10-26
Record ID: CVE-2026-109527.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 19:40 UTC. Ingestion is not an independent editorial investigation.

NVD status: Awaiting Analysis. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

Record JSON

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Record details

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