# CVE-2026-109527: Model Context Protocol Python SDK HTTP and OAuth endpoints allow memory exhaustion through unbounded request bodies

> Unauthenticated attackers can exhaust server memory by sending large request bodies to MCP Python SDK HTTP endpoints, causing denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Oct 2026
- **Updated:** 20 Oct 2026
- **Also known as:** GHSA-fmmv-w9g8-j3gc

## What is CVE-2026-109527?

CVE-2026-109527 is a high-severity denial of service vulnerability in modelcontextprotocol python-sdk, published on 14 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-109527?


## How do I fix CVE-2026-109527?

No fix has been published for CVE-2026-109527 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-109527 being exploited?

There is no known exploitation of CVE-2026-109527 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-109527 and fix it if it is affected.

What it is: CVE-2026-109527 is a high-severity denial of service vulnerability in modelcontextprotocol python-sdk, published on 14 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-109527 in the wild and no public exploit code.

Affected product: modelcontextprotocol python-sdk. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-109527/ (Markdown: https://insights.sbomify.com/CVE-2026-109527/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-109527
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-109527
- OSV: https://osv.dev/vulnerability/CVE-2026-109527

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-109527/
Summaries are generated and may contain mistakes; the official description above is the record.