---
id: CVE-2025-6515
title: >-
  The MCP SSE endpoint in oatpp-mcp returns an instance pointer as the session
  ID, which is not unique nor cryptographically secure
summary: >-
  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 l…
severity: medium
cvss: 6.8
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H'
cwe:
  - CWE-330
published: '2025-10-20'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T22:10:00.563'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-6515'
references:
  - url: >-
      https://research.jfrog.com/vulnerabilities/oatpp-mcp-prompt-hijacking-jfsa-2025-001494691/
    label: reefs@jfrog.com
tags:
  - nvd
epss: 0.00401
epssPercentile: 0.32257
ingestedAt: '2026-10-08T22:11:53.818Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.