CVE-2026-63118

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.

CVSS v4.0

6.9 MEDIUMCVSS: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

CVSS v4.0

6.9 MEDIUMCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N

EPSS

0.19% chance of exploitation in the next 30 days, 9th percentile

Published

2026-07-29

Proof-of-concept exploits (1)

• advisories/GHSA-rjr6-rcgv-9m7m

References

• CVE Record
• NVD entry

Related

• CVE-2026-63108
• CVE-2026-63123
• CVE-2026-63107
• CVE-2026-63135
• CVE-2026-63101
• CVE-2026-63188