How severe is CVE-2021-43991?

CVE-2021-43991 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2021-43991 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-43991?

CVE-2021-43991 affects Kentico Xperience. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-43991?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-43991 published?

CVE-2021-43991 was published on 2021-12-03 and last updated on 2026-06-17.

CVE-2021-43991

CVE-2021-43991 is a medium-severity vulnerability in Kentico Xperience with a CVSS 3.x base score of 6.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 6.8)
CVSS v2: 3.5
EPSS exploit prediction: 1% (42nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Kentico Xperience
Published: 2021-12-03
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-43991?: 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.
How severe is CVE-2021-43991?: CVE-2021-43991 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2021-43991 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-43991?: CVE-2021-43991 affects Kentico Xperience. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-43991?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-43991 published?: CVE-2021-43991 was published on 2021-12-03 and last updated on 2026-06-17.

References

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

Affected products (1)

cpe:2.3:a:kentico:xperience:*:*:*:*:*:*:*:*

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