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01 Record

CVE-2026-33946

MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay

HighPUBLISHEDCNA: GitHub_M
CNA base score8.2 CVSS v4.0CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
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02 Description

MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay

03 Exploitation and scoring

Exploitation
Public exploit code exists. CISA's assessment records a public proof of concept. That is not a report of exploitation in the wild.
SSVC decision
  • ExploitationpocPublic proof-of-concept exploit code exists. Not a report of exploitation in the wild.
  • AutomatableyesAn attacker can reliably automate reconnaissance through exploitation, so this scales.
  • Technical ImpactpartialSuccessful exploitation gives limited control of the vulnerable component.
CISA publishes the decision points, not a final SSVC decision. The decision also depends on mission and well-being impact, which is a property of your deployment rather than of the vulnerability.
EPSS probability
0.47% probability of exploitation activity in the next 30 days.
EPSS percentile
Equal to or higher than the score of 40.6% of scored records. A rank, not a probability.
NVD base score
8.2 (CVSS v4.0), scored by the NVD independently of the CNA.
NVD CVSS vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD analysis status
Analyzed. NVD last modified this record on 2026-10-26.
Red Hat severity
No Red Hat rating. Red Hat rates the CVEs that affect its products.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

04 Metadata

Published
2026-03-27 21:20Z7 MO AGO
Last updated
2026-03-30 18:42Z7 MO AGO
Reserved
2026-03-24
Assigning CNA
GitHub_M
Record state
PUBLISHED
Severity
High (CVSS 8.2)
CNA CVSS vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Weaknesses
  • CWE-384Session FixationCompound
  • CWE-639Authorization Bypass Through User-Controlled KeyBase
Data version
5.2
Document digest
a88d475a165622c1e6407ffc33ca293e0db4d2cb38ebd99dfd1a8d0ae0172644

05 Affected products

VendorProductVersionsPlatforms
modelcontextprotocolruby-sdk< 0.9.2—

06 References