CVE-2026-109527Model Context Protocol Python SDK HTTP and OAuth endpoints allow memory exhaustion through unbounded request bodies
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It affects modelcontextprotocol python-sdk. Add what you run to find out whether that includes you.
EPSS puts the chance of exploitation in the next 30 days at 0.70%, higher than 52% of scored CVEs.
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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 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Weakness (CWE)
- CWE-770
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- 0.70% (percentile 52)
- Assigned by
- GitHub_M
- NVD analysis
- Awaiting Analysis
- Record last updated
- Oct 14, 2026
- First seen by InfoSec Signals
- Oct 14, 2026
Affected products
modelcontextprotocol python-sdk modelcontextprotocol:python_sdk (from the name) | before 1.29.1; from 2.0.0a1, < 2.1.0 | CNA record |
References
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-fmmv-w9g8-j3gcx-refsource-confirm
- https://github.com/modelcontextprotocol/python-sdk/commit/03aaebd3aadb2567878dd811cb1f141454e8a080x-refsource-misc
- https://github.com/modelcontextprotocol/python-sdk/commit/4dc224fab201bdef2fd5a065976b7ca31420187cx-refsource-misc
- https://github.com/modelcontextprotocol/python-sdk/commit/57394b0548d1e2dc2dce8d67d84985769df3b8bbx-refsource-misc
- https://github.com/modelcontextprotocol/python-sdk/commit/5f0b6af9f2b0aad3be3ba5cbfe80a9e4ea32e189x-refsource-misc
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.29.1x-refsource-misc
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.1.0x-refsource-misc
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.