modelcontextprotocol ruby-sdk up to 0.9.1 streamable_http_transport.rb session fixiation

CVSS Meta Temp Score
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CTI Interest Score
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7.0$0-$5k0.00

Summaryinfo

A vulnerability identified as critical has been detected in modelcontextprotocol ruby-sdk up to 0.9.1. Impacted is an unknown function of the file streamable_http_transport.rb. Performing a manipulation results in session fixiation. This vulnerability is known as CVE-2026-33946. Remote exploitation of the attack is possible. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in modelcontextprotocol ruby-sdk up to 0.9.1. It has been classified as critical. This affects some unknown functionality of the file streamable_http_transport.rb. The manipulation with an unknown input leads to a session fixiation vulnerability. CWE is classifying the issue as CWE-384. Authenticating a user, or otherwise establishing a new user session, without invalidating any existing session identifier gives an attacker the opportunity to steal authenticated sessions. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-33946 since 03/24/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available.

Upgrading to version 0.9.2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-16866). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

Vendor

Name

Version

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 7.3
VulDB Meta Temp Score: 7.0

VulDB Base Score: 7.3
VulDB Temp Score: 7.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Session fixiation
CWE: CWE-384
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: ruby-sdk 0.9.2

Timelineinfo

03/24/2026 CVE reserved
03/27/2026 +3 days Advisory disclosed
03/27/2026 +0 days VulDB entry created
03/29/2026 +2 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-33946 (🔒)
GCVE (CVE): GCVE-0-2026-33946
GCVE (VulDB): GCVE-100-353985
EUVD: 🔒

Entryinfo

Created: 03/27/2026 23:05
Updated: 03/29/2026 05:12
Changes: 03/27/2026 23:05 (68), 03/29/2026 05:12 (1)
Complete: 🔍
Cache ID: 216:190:103

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