CVE-2026-67430: modelcontextprotocol ruby-sdk
Vulnerability summary
CVE-2026-67430 is a medium (CVSS 5.3) vulnerability in modelcontextprotocol ruby-sdk. EPSS estimates a 0.51% chance of exploitation in the next 30 days, higher than 42% of scored vulnerabilities.
Timeline
- 29-07-2026PublishedVulnerability first disclosed.
- 30-07-2026Last modifiedVulnerability information updated.
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 does not expire sessions by default, so repeated initialize requests retain unbounded ServerSession objects and can exhaust process memory. This issue is fixed in version 0.23.0.
CVSS metrics
3 scores · 3 sources · 1 version- OSV · RubygemsEcosystem advisory · calculated5.3MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- NVDNIST5.3MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS trend
Probability
0.51%
Chance of exploitation in the next 30 days
Percentile
42%
Versus all other CVEs
30-day change
+0.20 pp
From 0.31% on 20-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-401Missing Release of Memory after Effective LifetimeThe product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.
- CWE-770Allocation of Resources Without Limits or ThrottlingThe product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
Affected systems
Modelcontextprotocol1 product
- ruby-sdk< 0.23.0
RubyGems1 product
- mcp< 0.23.0
2 vendors · 2 products
References
5 links- github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-52jp-gj8w-j6xhX Refsource CONFIRMWEB
