CVE-2026-528697.1HighCWE-639

CVE-2026-52869: MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal

modelcontextprotocol · python-sdk

Affected: modelcontextprotocol python-sdk · Exploitation: unlikely (under 1%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

0.5%probability of exploitation in the next 30 days

45th percentile

050100

Higher than 45% of scored CVEs

7.1HighCVSS 3.1

LowMediumHighCrit.

DescriptionCVE.org

The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.27.2, the SSE and stateful Streamable HTTP transports mcp.server.sse.SseServerTransport and mcp.server.streamable_http_manager.StreamableHTTPSessionManager route requests to existing sessions using only the session_id query parameter or Mcp-Session-Id header without verifying the authenticated principal that created the session, allowing a different bearer-token-authenticated client with a known session ID to inject JSON-RPC messages into that session. This issue is fixed in version 1.27.2.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

modelcontextprotocol · python-sdk< 1.27.2

On the Atlas

Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.

Open the Atlas

Exploitation: Unlikely (under 1%). EPSS under 1%, or no score yet.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Insecure Direct Object Reference
Vendor: modelcontextprotocol
Published: July 2026
Band: Unlikely (under 1%), July 2026

CoverageNo articles yet

No CyberSIXT article names CVE-2026-52869 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.