CVE-2026-59951Network attack vectorHinoki check available

DoS via unbounded HTTP session retention

Published Oct 14, 2026 · Updated Oct 14, 2026

Session retention in MCP Python SDK Streamable HTTP servers allows remote attackers to exhaust memory via ordinary requests. StreamableHTTPSessionManager retains session entries and parsed initialize parameters without expiration or a session-count limit, including entries for ended or refused sessions. Endpoint access and stateful mode, the default, are required; the advisory does not specify whether exhaustion hangs or crashes the server.

CVSS severity7.5
High
EPSS probability0.46%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Session retention in MCP Python SDK Streamable HTTP servers allows remote attackers to exhaust memory via ordinary requests. StreamableHTTPSessionManager retains session entries and parsed initialize parameters without expiration or a session-count limit, including entries for ended or refused sessions. Endpoint access and stateful mode, the default, are required; the advisory does not specify whether exhaustion hangs or crashes the server.

The record

CVE
CVE-2026-59951
Published
Oct 14, 2026
Updated
Oct 14, 2026
Vendor
Model Context Protocol
Product
MCP Python SDK
Classifications
CWE-770, CWE-772, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 14, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 1.8.0, < 1.30.0
  2. Affected versionversion=>= 2.0.0, < 2.2.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Model Context Protocol · MCP Python SDKversion=>= 1.8.0, < 1.30.0; version=>= 2.0.0, < 2.2.0

Published CVSS scores

7.5Model Context ProtocolCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
CWE-772Missing Release of Resource after Effective Lifetime
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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