CVE-2026-33946
Published: 27 March 2026
Summary
CVE-2026-33946 is a high-severity Session Fixation (CWE-384) vulnerability in Lfprojects Mcp Ruby Sdk. Its CVSS base score is 8.2 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Web Session Cookie (T1550.004); ranked at the 36.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
This vulnerability is AI-related — categorised as AI Agent Protocols and Integrations; in the Protocol-Specific Risks risk domain.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-16866
Vulnerability details
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…
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the victim's Server-Sent Events (SSE) stream and intercept all real-time data. Version 0.9.2 contains a patch.
- CWE(s)
AI Security AnalysisAI
- AI Category
- AI Agent Protocols and Integrations
- Risk Domain
- Protocol-Specific Risks
- OWASP Top 10 for LLMs 2025
- None mapped
- Classification Reason
- Matched keywords: mcp, model context protocol
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Session ID hijacking of SSE stream directly enables use of stolen web session material for impersonation.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Session termination after a set interval shortens the usable lifetime of a fixed session identifier, making successful exploitation of session fixation more difficult.
Per-request decision making makes it harder to bypass authorization using user-controlled keys without proper validation in the decision process.
Consistent enforcement of approved authorizations makes bypassing via user-controlled keys ineffective.
Re-authentication typically forces issuance of a new session, limiting the window for exploitation of a previously fixed session identifier.
Enforces proper session ID generation and binding, preventing fixation of a known session token.