CVE-2026-33946: MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients

Q: How do I fix CVE-2026-33946?

mcp ruby sdk: upgrade to 0.9.2. Exact commands for each OS are on this page.

Q: Is CVE-2026-33946 being exploited?

CVE-2026-33946 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-33946 affect?

CVE-2026-33946 affects mcp ruby sdk. Severity is medium (CVSS 5.9). MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to version 0.9.2, the Ruby SDK's streamable_http_transport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a v

Q: How urgent is CVE-2026-33946?

Priority 41/100. Public exploit reference; Remotely exploitable, no login, no user action

This week

MEDIUM 5.9REMOTEUPGRADE

CVE-2026-33946 is a medium-severity flaw (CVSS 5.9) affecting mcp ruby sdk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to version 0.9.2, the Ruby SDK's streamable_http_transport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a valid session ID can completely hijack the victim's Server-Sent Events (SSE) stream and intercept all real-time data. Version 0.9.2 contains a patch.

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 59%)
CISA exploited list	No
Weakness	CWE-384, CWE-639
Published	2026-03-27
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: lfprojects

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-27 22:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

lfprojects mcp ruby sdk UPGRADE

Affected: < 0.9.2

Fixed in: 0.9.2

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mcp-ruby-sdk || rpm -q mcp-ruby-sdk || mcp-ruby-sdk --version

2. UPGRADE to 0.9.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mcp-ruby-sdk

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mcp-ruby-sdk

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-33946?

mcp ruby sdk: upgrade to 0.9.2. Exact commands for each OS are on this page.

Is CVE-2026-33946 being exploited?

CVE-2026-33946 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-33946 affect?

CVE-2026-33946 affects mcp ruby sdk. Severity is medium (CVSS 5.9). MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to version 0.9.2, the Ruby SDK's streamable_http_transport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a v

How urgent is CVE-2026-33946?

Priority 41/100. Public exploit reference; Remotely exploitable, no login, no user action

Software pages

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References

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