CVE-2021-43991Public exploitNetwork attack vector

Authenticated stored XSS via avatar upload

Published Dec 3, 2021 · Updated Aug 4, 2024

Cross-site scripting in Kentico Xperience CMS 13.0 through 13.0.43 allows remote authenticated users to execute script in other users’ sessions. The avatar upload accepts an image filename while trusting a user-supplied image/* MIME type, then serves the stored bytes with that type and an inline Content-Disposition header, allowing an SVG payload to execute JavaScript when another user views the avatar. Exploitation requires a registered account able to upload an avatar and a victim who loads the rendered image; documented effects include session hijacking, account takeover, and sensitive-data access.

CVSS severity6.8
Medium
EPSS probability0.55%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Kentico Xperience CMS 13.0 through 13.0.43 allows remote authenticated users to execute script in other users’ sessions. The avatar upload accepts an image filename while trusting a user-supplied image/* MIME type, then serves the stored bytes with that type and an inline Content-Disposition header, allowing an SVG payload to execute JavaScript when another user views the avatar. Exploitation requires a registered account able to upload an avatar and a victim who loads the rendered image; documented effects include session hijacking, account takeover, and sensitive-data access.

The record

CVE
CVE-2021-43991
Published
Dec 3, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 3, 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

3.5NISTAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NISTCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
6.8AppCheck Ltd.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:N/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')
T1059.007JavaScript

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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