Is CVE-2026-63119 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-63119 being exploited in the wild.

How severe is CVE-2026-63119?

Medium severity, with a CVSS score of 6.2, published 29 July 2026.

Which products and versions are affected?

mcp (RubyGems) ECOSYSTEM:introduced=0,fixed=0.23.0.

Is there a fix for CVE-2026-63119?

Yes. mcp (RubyGems): upgrade to 0.23.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-63119 attacked?

It is attacked with local access, in a software library.

Am I affected by CVE-2026-63119?

Check whether you run mcp (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-63119: modelcontextprotocol ruby-sdk memory exhaustion in Stdio transports

CVE-2026-63119 · Severity: medium · CVSS 6.2 · Published 2026-07-29

The Model Context Protocol (MCP) Ruby SDK is used to build applications that communicate with AI models and tools. A vulnerability in how it handles data input allows a connected process to send an endless stream of data without a line break, causing the application to consume all available system memory. This can lead to a denial-of-service (DoS) where the application or the entire host system crashes due to memory exhaustion.

Technologies: mcp (RubyGems). Vendors: RubyGems.

Quick answers

Is CVE-2026-63119 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-63119 being exploited in the wild.
How severe is CVE-2026-63119?: Medium severity, with a CVSS score of 6.2, published 29 July 2026.
Which products and versions are affected?: mcp (RubyGems) ECOSYSTEM:introduced=0,fixed=0.23.0.
Is there a fix for CVE-2026-63119?: Yes. mcp (RubyGems): upgrade to 0.23.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-63119 attacked?: It is attacked with local access, in a software library.
Am I affected by CVE-2026-63119?: Check whether you run mcp (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

mcp (RubyGems): upgrade to 0.23.0 or later
```
bundle update mcp
```

Technical details

The vulnerability exists in `MCP::Server::Transports::StdioTransport` and `MCP::Client::Stdio` due to the use of Ruby's `IO#gets` without a `limit` argument. Because `gets` continues to accumulate bytes into a single Ruby String until a newline character is encountered, a malicious or misconfigured peer can stream data indefinitely to exhaust process memory. This is particularly critical in sandboxed environments where a restricted child process could crash an unrestricted host process by piping unbounded data to its stdout. The issue was resolved in version 0.23.0 by introducing a configurable maximum line length (defaulting to 4 MiB) and treating over-limit lines as transport errors.

Affected products

modelcontextprotocol mcp <= 0.22.0

Identifiers

CVE-2026-63119
GHSA-7683-3w9x-ch42

Timeline

2026-07-08: patched: Fixed in version 0.23.0
2026-07-29: advisory: NVD publication date
2026-07-30: disclosed: GitHub Advisory published

References

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