CVE-2026-109527: CWE-770: Allocation of Resources Without Limits or Throttling in modelcontextprotocol python-sdk
Description
CVE-2026-109527 affects the Model Context Protocol Python SDK in versions before 1.29.1 and from 2.0.0a1 up to but not including 2.1.0. The vulnerability involves the Streamable HTTP session manager, SSE message endpoint, and OAuth authorization-server routes buffering complete HTTP request bodies without enforcing size limits. This allows an unauthenticated remote attacker to send large request bodies that consume excessive memory, potentially exhausting server memory or causing server termination. Deployments with upstream request-size limits or using stdio-only servers are not affected. The issue is fixed in versions 1.29.1 and 2.1.0.
CVSS v3.1
Score 7.5high
Affected software
modelcontextprotocol
python-sdk
pkg:pypi/modelcontextprotocol-python-sdkRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The Model Context Protocol Python SDK versions prior to 1.29.1 and from 2.0.0a1 through 2.0.1 have a resource exhaustion vulnerability (CWE-770) due to lack of limits on buffered HTTP request body sizes in certain components (Streamable HTTP session manager, SSE message endpoint, OAuth authorization-server routes). An unauthenticated remote client can exploit this by sending large request bodies that consume multiple times their size in process memory, leading to repeated memory exhaustion or server termination. The vulnerability does not affect stdio-only servers or deployments with effective upstream request-size limits. Applications using StreamableHTTPServerTransport directly must enforce their own limits. The vulnerability is resolved in versions 1.29.1 and 2.1.0 of the SDK.
Potential Impact
An unauthenticated remote attacker can cause a denial of service by exhausting server memory or terminating the server process through sending large HTTP request bodies to affected endpoints. There is no impact on confidentiality or integrity. The attack requires network access to the vulnerable endpoints.
Mitigation Recommendations
Upgrade to Model Context Protocol Python SDK version 1.29.1 or later, or 2.1.0 or later, where the vulnerability is fixed. Deployments using stdio-only servers or with effective upstream request-size limits are not affected. Applications using StreamableHTTPServerTransport directly should implement their own request size limits to mitigate this issue.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-10-12T19:11:21.789Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6acfc4752cdf04f6569de054
Added to database: 10/14/2026, 18:05:41 UTC
Last enriched: 10/14/2026, 18:18:32 UTC
Last updated: 10/14/2026, 19:00:29 UTC
Views: 8
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.