CVE-2021-39609Public exploitNetwork attack vector

Stored XSS via unsanitized SVG image upload

Published Aug 23, 2021 · Updated Aug 4, 2024

Stored cross-site scripting in FlatCore-CMS 2.0.7 allows remote authenticated users to execute scripts via an uploaded SVG image. The image uploader accepts an SVG containing a script and publishes it under content/images without neutralizing the active content. An authenticated upload and a later browser request for the SVG are required; the script runs in the site's origin and can access browser-visible session data or alter page content.

CVSS severity5.4
Medium
EPSS probability1.70%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored cross-site scripting in FlatCore-CMS 2.0.7 allows remote authenticated users to execute scripts via an uploaded SVG image. The image uploader accepts an SVG containing a script and publishes it under content/images without neutralizing the active content. An authenticated upload and a later browser request for the SVG are required; the script runs in the site's origin and can access browser-visible session data or alter page content.

The record

CVE
CVE-2021-39609
Published
Aug 23, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1539
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 23, 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

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

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-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1539Steal Web Session Cookie

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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