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VulnerabilityPublished

CVE-2025-6515: oatpp-mcp · Weak Randomness

Affects oatpp-mcpSource CVE Database V5

0

Not known to be exploited · CVSS 6.8 Medium.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score
6.8Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 34% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 20 Oct 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Affected software

ProductAffectedFixed in
oatpp oatpp-mcpAffected
  • =0
Fixed in–

AI-suggested

To mitigate CVE-2025-6515, organizations should first assess their deployment of oatpp-mcp and identify exposed MCP SSE endpoints. Immediate mitigation includes restricting network access to the oatpp-mcp server to trusted hosts only, using network segmentation and firewall rules to limit attacker access. Implementing Transport Layer Security (TLS) can help protect session data in transit, although it does not fix the session ID predictability itself. Developers should avoid using instance pointers or any predictable values as session identifiers and instead implement cryptographically secure random session IDs with sufficient entropy. Until an official patch is released, consider deploying application-layer filters or proxies that validate session IDs against a secure session management system. Monitoring and logging MCP session activity for anomalies can help detect attempted hijacking. Finally, coordinate with the oatpp project maintainers for updates and apply patches promptly once available.

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.

References

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