Description
MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem does not bind a session ID to a session owner, allowing an attacker with a stolen session ID to send tools/call requests that execute in the victim's session. This issue is fixed in version 0.23.0.
References (3)
Core 3
Core References
X_Refsource_Confirm x_refsource_confirm
https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwv
X_Refsource_Misc x_refsource_misc
https://github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356
X_Refsource_Misc x_refsource_misc
https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0
Scores
CVSS v4
8.3
EPSS
0.0028
EPSS Percentile
19.9%
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CISA SSVC
Vulnrichment
Exploitation
poc
Automatable
yes
Technical Impact
total
Details
CWE
CWE-284
Status
published
Products (2)
modelcontextprotocol/ruby-sdk
< 0.23.0
rubygems/mcp
0 - 0.23.0RubyGems
Published
Jul 29, 2026
Tracked Since
Jul 30, 2026