CVE-2026-33946 MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay
Attackers can hijack SSE streams and intercept real-time data by replaying session IDs in the MCP Ruby SDK.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33946?
CVE-2026-33946 is a high-severity authentication bypass vulnerability in modelcontextprotocol ruby-sdk, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to version 0.9.2, the Ruby SDK's streamable_http_transport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a valid session ID can completely hijack the victim's Server-Sent Events (SSE) stream and intercept all real-time data. Version 0.9.2 contains a patch.
Which versions are affected by CVE-2026-33946?
2 open source packages ship an affected version, including mcp. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
mcp RubyGems | All versions | 0.9.2 |
mcp RubyGems | All versions | 0.9.2 |
Products include Lfprojects Mcp Ruby Sdk.
How do I fix CVE-2026-33946?
Upgrade mcp to 0.9.2 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-33946 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33946 exists.
Sources
Also known as GHSA-qvqr-5cv7-wh35.