Vulnerability in Oatpp Oatpp-Mcp

CVE-2025-6515

The MCP SSE endpoint in oatpp-mcp returns an instance pointer as the session ID, which is not unique nor cryptographically secure. This allows network attackers with access to the oatpp-mcp server to guess future session IDs and hijack legitimate client MCP sessions, returning malicious responses from the oatpp-mcp server.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 6.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (32.1th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 32nd percentile — 32.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2025-6515: held from 0.004 to 0.004.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2025-6515?
CVE-2025-6515 is a medium-severity vulnerability in Oatpp Oatpp-Mcp, classified under Use of Insufficiently Random Values. CVSS score: 6.8/10. Published 2025-10-20.
How severe is CVE-2025-6515?
Medium severity. CVSS v3 base score is 6.8 out of 10.