CVE-2026-63118Public exploitNetwork attack vector

Local tool invocation via missing origin validation

Published Jul 29, 2026 · Updated Jul 29, 2026

Origin validation errors in the MCP Ruby SDK before 0.23.0 allow remote attackers to invoke local server tools through DNS rebinding. MCP::Server::Transports::StreamableHTTPTransport dispatches JSON-RPC requests without checking attacker-controlled Host or Origin headers. Exploitation requires a victim to open a malicious page while a vulnerable Streamable HTTP server is reachable; exposed tools determine whether data is read or local actions execute.

CVSS severity6.9
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Origin validation errors in the MCP Ruby SDK before 0.23.0 allow remote attackers to invoke local server tools through DNS rebinding. MCP::Server::Transports::StreamableHTTPTransport dispatches JSON-RPC requests without checking attacker-controlled Host or Origin headers. Exploitation requires a victim to open a malicious page while a vulnerable Streamable HTTP server is reachable; exposed tools determine whether data is read or local actions execute.

The record

CVE
CVE-2026-63118
Published
Jul 29, 2026
Updated
Jul 29, 2026
Vendor
Model Context Protocol
Product
Ruby SDK
Classifications
CWE-350, CWE-346, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 29, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 29, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.23.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Model Context Protocol · Ruby SDKversion=< 0.23.0

Published CVSS scores

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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-350Reliance on Reverse DNS Resolution for a Security-Critical Action
CWE-346Origin Validation Error
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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