CVE-2020-20691Public exploitNetwork attack vector

Stored XSS via crafted file rename

Published Sep 27, 2021 · Updated Aug 4, 2024

Unrestricted file upload in Monstra CMS 3.0.4 allows remote authenticated users to run arbitrary scripts in visitors' browsers. The Files Manager accepts a file under a permitted extension, then trusts a crafted rename value containing quotes and an HTML suffix, leaving active HTML in the web-accessible uploads directory. Access to the Files Manager and a victim opening the uploaded file are required; successful exploitation exposes browser data and permits actions in that visitor's session.

CVSS severity6.5
Medium
EPSS probability0.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unrestricted file upload in Monstra CMS 3.0.4 allows remote authenticated users to run arbitrary scripts in visitors' browsers. The Files Manager accepts a file under a permitted extension, then trusts a crafted rename value containing quotes and an HTML suffix, leaving active HTML in the web-accessible uploads directory. Access to the Files Manager and a victim opening the uploaded file are required; successful exploitation exposes browser data and permits actions in that visitor's session.

The record

CVE
CVE-2020-20691
Published
Sep 27, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-434, T1189
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:N

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
T1189Drive-by Compromise

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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