CVE-2025-6515
Reuse of session IDs in oatpp-mcp leads to session hijacking and prompt hijacking by remote attackers
CVE-2025-6515 is a medium vulnerability (CVSS 6.8) in Oatpp Oatpp-mcp, published October 20, 2025. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.40%, the 34th percentile. No source names a fixed version.
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- None
- User interaction
- Required
What an attacker can affect
- Confidentiality
- None
- Integrity
- High
- Availability
- High
Exploit likelihood
What each source reports
CVE List Score used
Reuse of session IDs in oatpp-mcp leads to session hijacking and prompt hijacking by remote attackers
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.
- Record
CVE-2025-6515- CVSS 3.1
- 6.8 Medium
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H - Weakness
- CWE-330
- Updated
- 2026-11-02
EUVDEUVD-2025-35077
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.
- Record
EUVD-2025-35077- CVSS 3.1
- 6.8 Medium
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-rvw9-mm8q-456q
The MCP SSE endpoint in oatpp-mcp returns an instance pointer as the session ID, which is not...
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.
- Record
GHSA-rvw9-mm8q-456q- CVSS 3.1
- 6.8 Medium
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H - Weakness
- CWE-330
- Updated
- 2026-11-02
NVD
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.
- Record
CVE-2025-6515- CVSS 3.1
- 6.8 Medium
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H - Weakness
- CWE-330
- Updated
- 2026-11-02
Affected products
History
| When | Changed | Sources |
|---|---|---|
| 2026-11-02 | created | CVE List, EUVD, GitHub Advisories, NVD |