Session Hijacking Vulnerability in Ruby SDK for Model Context Protocol
CVE-2026-33946

8.2HIGH

Key Information:

Vendor

Modelcontextprotocol

Status
Ruby-sdk
Vendor
CVE Published:
27 March 2026

What is CVE-2026-33946?

The Ruby SDK for Model Context Protocol contains a session hijacking vulnerability in its streamable_http_transport.rb implementation. An attacker who obtains a valid session ID can gain unauthorized access to a victim's Server-Sent Events (SSE) stream, allowing them to intercept all real-time data transmitted over this channel. This issue has been addressed in version 0.9.2, which includes necessary patches to mitigate the risk.

Affected Version(s)

ruby-sdk < 0.9.2

References

https://github.com/modelcontextprotocol/ruby-sdk/security...
x_refsource_CONFIRM
https://github.com/modelcontextprotocol/ruby-sdk/commit/d...
x_refsource_MISC
https://hackerone.com/reports/3556146
x_refsource_MISC

CVSS V4

Score:
8.2
Severity:
HIGH
Confidentiality:
High
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.