CVE-2025-9800Public exploitNetwork attack vector

Stored XSS via unrestricted HTML file upload

Published Sep 1, 2025 · Updated Sep 2, 2025

Unrestricted file upload in Sim allows remote authenticated users to store malicious HTML through the file upload API. The POST handler in apps/sim/app/api/files/upload/route.ts accepts the supplied filename extension and writes or forwards the file without an allowlist. A valid session is required, and script execution occurs only when another user opens the served HTML file.

CVSS severity6.3
Medium
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

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Summary

What happened

Unrestricted file upload in Sim allows remote authenticated users to store malicious HTML through the file upload API. The POST handler in apps/sim/app/api/files/upload/route.ts accepts the supplied filename extension and writes or forwards the file without an allowlist. A valid session is required, and script execution occurs only when another user opens the served HTML file.

The record

CVE
CVE-2025-9800
Published
Sep 1, 2025
Updated
Sep 2, 2025
Vendor
SimStudioAI
Product
Sim
Classifications
CWE-434, CWE-284, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 1, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 2, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=ed9b9ad83f1a7c61f4392787fb51837d34eeb0af

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

SimStudioAI · Simversion=ed9b9ad83f1a7c61f4392787fb51837d34eeb0af

Published CVSS scores

2.1VulDBCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
6.5VulDBAV:N/AC:L/Au:S/C:P/I:P/A:P
6.3VulDBCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
CWE-284Improper Access Control
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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