CVE-2026-67432 MCP Ruby SDK: Unbounded JSON-RPC request body causes uncontrolled memory allocation in StreamableHTTPTransport
An unauthenticated remote attacker can exhaust process memory by sending large JSON-RPC requests to the MCP Ruby SDK, causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-67432?
CVE-2026-67432 is a high-severity denial of service vulnerability in modelcontextprotocol ruby-sdk, published on 29 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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 reads and parses an entire JSON-RPC POST body without a size limit, allowing an unauthenticated remote attacker to exhaust process memory. This issue is fixed in version 0.23.0.
Weakness: CWE-770
Which versions are affected by CVE-2026-67432?
2 open source packages ship an affected version, including mcp.
| Package | Affected | Fixed in |
|---|---|---|
mcp RubyGems | All versions | 0.23.0 |
mcp RubyGems | All versions | 0.23.0 |
How do I fix CVE-2026-67432?
Upgrade mcp to 0.23.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-67432 being exploited?
There is no known exploitation of CVE-2026-67432 in the wild and no public exploit code.
Sources
Also known as GHSA-h669-8m4g-r2hc.