CVE-2025-6515 Reuse of session IDs in oatpp-mcp leads to session hijacking and prompt hijacking by remote attackers
Remote attackers can hijack MCP sessions by guessing predictable session IDs, allowing them to intercept and modify server responses.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2025-6515?
CVE-2025-6515 is a medium-severity authentication bypass vulnerability in oatpp-mcp, published on 20 Oct 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-330
Which versions are affected by CVE-2025-6515?
How do I fix CVE-2025-6515?
No fix has been published for CVE-2025-6515 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2025-6515 being exploited?
There is no known exploitation of CVE-2025-6515 in the wild and no public exploit code.
Sources
Also known as GHSA-rvw9-mm8q-456q.