CVE-2021-39136Network attack vector

Stored XSS via unescaped uploaded-file URL

Published Aug 25, 2021 · Updated Aug 4, 2024

Stored XSS in baserCMS before 4.5.1 allows remote authenticated users to execute JavaScript through a crafted uploaded filename. The Uploader plugin's two ajax_image.php views placed a filename-derived URL into link markup without HTML escaping, allowing attribute injection. Exploitation requires access to the management file uploader and a victim who views the stored entry; resulting script execution can alter page content or expose cookies.

CVSS severity8.7
High
EPSS probability0.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Stored XSS in baserCMS before 4.5.1 allows remote authenticated users to execute JavaScript through a crafted uploaded filename. The Uploader plugin's two ajax_image.php views placed a filename-derived URL into link markup without HTML escaping, allowing attribute injection. Exploitation requires access to the management file uploader and a victim who views the stored entry; resulting script execution can alter page content or expose cookies.

The record

CVE
CVE-2021-39136
Published
Aug 25, 2021
Updated
Aug 4, 2024
Vendor
baserCMS Users Community
Product
baserCMS
Classifications
CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 25, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=< 4.5.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

baserCMS Users Community · baserCMSversion=< 4.5.1

Published CVSS scores

3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
8.7GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/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 exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo