CVE-2021-26539

Name: CVE-2021-26539
Creator: NVD / NIST
Published: 2021-02-08T17:15:13.673+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 1.95%

Last modified Jun 17, 2026

CVE-2021-26539 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. Apostrophe Technologies sanitize-html before 2.3.1 does not properly handle internationalized domain name (IDN) which could allow an attacker to bypass hostname whitelist validation set by the "allowedIframeHostnames" option.. EPSS estimates a 1.95% chance of exploitation in the next 30 days.

Description

Apostrophe Technologies sanitize-html before 2.3.1 does not properly handle internationalized domain name (IDN) which could allow an attacker to bypass hostname whitelist validation set by the "allowedIframeHostnames" option.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

1.95%

77.7th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Apostrophecms	Sanitize-Html	< 2.3.1

References

https://advisory.checkmarx.net/advisory/CX-2021-4308Exploit, Third Party Advisory
https://github.com/apostrophecms/sanitize-html/blob/main/CHANGELOG.md#231-2021-01-22Release Notes, Third Party Advisory
https://github.com/apostrophecms/sanitize-html/pull/458Patch, Third Party Advisory
https://advisory.checkmarx.net/advisory/CX-2021-4308Exploit, Third Party Advisory
https://github.com/apostrophecms/sanitize-html/blob/main/CHANGELOG.md#231-2021-01-22Release Notes, Third Party Advisory
https://github.com/apostrophecms/sanitize-html/pull/458Patch, Third Party Advisory

Timeline

Published: Feb 8, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-26539?

How severe is CVE-2021-26539?

CVE-2021-26539 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 1.95% probability of exploitation in the next 30 days.

How do I fix CVE-2021-26539?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-26539?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST