CVE-2026-63118
MEDIUMMCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protection
Title source: cnaDescription
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 validate the HTTP Host or Origin request headers, which allows a malicious browser page to use DNS rebinding to reach a locally running MCP server and invoke exposed tools. 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-rjr6-rcgv-9m7m
X_Refsource_Misc x_refsource_misc
https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b29464b89091816446ff7a
X_Refsource_Misc x_refsource_misc
https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0
Scores
CVSS v4
6.9
EPSS
0.0020
EPSS Percentile
9.9%
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:N/VA:N/SC:H/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
no
Technical Impact
partial
Details
CWE
CWE-346
CWE-350
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