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01 Record

CVE-2026-59951

MCP Python SDK: Unbounded Session Accumulation in StreamableHTTP Transport Enables Resource Exhaustion

MediumPUBLISHEDCNA: GitHub_M
CNA base score6.9 CVSS v4.0CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
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02 Description

MCP Python SDK: Unbounded Session Accumulation in StreamableHTTP Transport Enables Resource Exhaustion

03 Exploitation and scoring

Exploitation
Assessed, none found. CISA's assessment recorded neither public exploit code nor evidence of exploitation when it was made.
SSVC decision
  • ExploitationnoneCISA recorded no public exploit code and no evidence of exploitation.
  • 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
0.45% probability of exploitation activity in the next 30 days.
EPSS percentile
Equal to or higher than the score of 39.4% of scored records. A rank, not a probability.
NVD base score
6.9 (CVSS v4.0), scored by the NVD independently of the CNA.
NVD CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/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
Awaiting Analysis. NVD last modified this record on 2026-10-16.
Red Hat severity
Important. Red Hat's rating for its own products, not a CVSS rating.

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
2026-10-14 16:22Z14 DAYS AGO
Last updated
2026-10-15 15:07Z13 DAYS AGO
Reserved
2026-07-07
Assigning CNA
GitHub_M
Record state
PUBLISHED
Severity
Medium (CVSS 6.9)
CNA CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Weaknesses
  • CWE-400Uncontrolled Resource ConsumptionClass
  • CWE-772Missing Release of Resource after Effective LifetimeBase
Data version
5.2
Document digest
a3d5321a996662a5a7fd756ab500ed993d04f3fae4c06dc6371f44bea8b893a8

05 Affected products

VendorProductVersionsPlatforms
modelcontextprotocolpython-sdk>= 1.8.0, < 1.30.0, >= 2.0.0, < 2.2.0—

06 References