Allocation of Resources Without Limits or Throttling in MCP Python SDK - CVE-2026-109527
Published: November 9, 2026
Vulnerability identifier: #VU163094
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-109527
CWE-ID: CWE-770
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an unauthenticated remote attacker to exhaust an MCP Python SDK server's memory and take it offline.
The vulnerability exists due to unbounded request body buffering in HTTP transports and OAuth endpoints when processing oversized requests. An unauthenticated remote attacker can send a large request to a reachable OAuth endpoint or a server using default unauthenticated access, causing repeated denial of service where no upstream request size limit applies.
Affected software
MCP Python SDK
How to mitigate CVE-2026-109527
Install security update from vendor's website.
MCP Python SDK - addressed in versions 1.29.1, 2.1.0