modelcontextprotocol ruby-sdk up to 0.22.x StreamableHTTPTransport dns rebinding

Summaryinfo

A vulnerability has been found in modelcontextprotocol ruby-sdk up to 0.22.x and classified as critical. Affected by this issue is the function MCP::Server::Transports::StreamableHTTPTransport of the component StreamableHTTPTransport. The manipulation leads to dns rebinding. This vulnerability is referenced as CVE-2026-63118. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability, which was classified as critical, has been found in modelcontextprotocol ruby-sdk up to 0.22.x. This issue affects the function MCP::Server::Transports::StreamableHTTPTransport of the component StreamableHTTPTransport. The manipulation with an unknown input leads to a dns rebinding vulnerability. Using CWE to declare the problem leads to CWE-350. The product performs reverse DNS resolution on an IP address to obtain the hostname and make a security decision, but it does not properly ensure that the IP address is truly associated with the hostname. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-63118 since 07/15/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1583.002 according to MITRE ATT&CK.

Upgrading to version 0.23.0 eliminates this vulnerability.

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

• Programming Language Software

Vendor

• modelcontextprotocol

Name

• ruby-sdk

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8
• 0.9
• 0.10
• 0.11
• 0.12
• 0.13
• 0.14
• 0.15
• 0.16
• 0.17
• 0.18
• 0.19
• 0.20
• 0.21
• 0.22

Website

• Product: https://github.com/modelcontextprotocol/ruby-sdk/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Discussion