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01 Record

CVE-2025-62800

FastMCP vulnerable to reflected XSS in client's callback page

MediumPUBLISHEDCNA: GitHub_M
CNA base score5.3 CVSS v4.0CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

02 Description

FastMCP vulnerable to reflected XSS in client's callback page

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.
  • AutomatablenoAt least one step from reconnaissance to exploitation cannot be reliably automated.
  • 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
0.27% probability of exploitation activity in the next 30 days.
EPSS percentile
Equal to or higher than the score of 19.8% of scored records. A rank, not a probability.
NVD base score
5.3 (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:P/VC:N/VI:N/VA:N/SC:L/SI:L/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 2026-10-08.
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
2025-10-28 21:34Z1 YR AGO
Last updated
2025-10-29 15:52Z12 MO AGO
Reserved
2025-10-22
Assigning CNA
GitHub_M
Record state
PUBLISHED
Severity
Medium (CVSS 5.3)
CNA CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Weaknesses
  • CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')Base
Data version
5.2
Document digest
545d927339b8cf4f27f3201e086797fb48a4a309da99ca3ac30f2a3e8ab4f0a1

05 Affected products

VendorProductVersionsPlatforms
jlowinfastmcp< 2.13.0—

06 References