CVE-2021-41258: Kirby is an open source file structured CMS. In affected versions Kirby's blocks field stores structured data for each block. This data is then used i...

Description

Kirby is an open source file structured CMS. In affected versions Kirby's blocks field stores structured data for each block. This data is then used in block snippets to convert the blocks to HTML for use in your templates. We recommend to escape HTML special characters to protect against cross-site scripting (XSS) attacks. The default snippet for the image block unfortunately did not use our escaping helper. This made it possible to include malicious HTML code in the source, alt and link fields of the image block, which would then be displayed on the site frontend and executed in the browsers of site visitors and logged in users who are browsing the site. Attackers must be in your group of authenticated Panel users in order to exploit this weakness. Users who do not make use of the blocks field are not affected. This issue has been patched in Kirby version 3.5.8 by escaping special HTML characters in the output from the default image block snippet. Please update to this or a later version to fix the vulnerability.

Metrics

CVSS 3.1

5.4/10

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

EPSS Probability

0.78%

51.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Getkirby	Kirby	>= 3.5.0, <= 3.5.7.1

References

https://github.com/getkirby/kirby/pull/3510Patch, Third Party Advisory
https://github.com/getkirby/kirby/releases/tag/3.5.8Release Notes, Third Party Advisory
https://github.com/getkirby/kirby/security/advisories/GHSA-cq58-r77c-5jjwThird Party Advisory
https://github.com/getkirby/kirby/pull/3510Patch, Third Party Advisory
https://github.com/getkirby/kirby/releases/tag/3.5.8Release Notes, Third Party Advisory
https://github.com/getkirby/kirby/security/advisories/GHSA-cq58-r77c-5jjwThird Party Advisory

Timeline

Published: Nov 16, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-41258?

Kirby is an open source file structured CMS. In affected versions Kirby's blocks field stores structured data for each block. This data is then used in block snippets to convert the blocks to HTML for use in your templates. We recommend to escape HTML special characters to protect against cross-site scripting (XSS) attacks. The default snippet for the image block unfortunately did not use our escaping helper. This made it possible to include malicious HTML code in the source, alt and link fields of the image block, which would then be displayed on the site frontend and executed in the browsers of site visitors and logged in users who are browsing the site. Attackers must be in your group of authenticated Panel users in order to exploit this weakness. Users who do not make use of the blocks field are not affected. This issue has been patched in Kirby version 3.5.8 by escaping special HTML characters in the output from the default image block snippet. Please update to this or a later version to fix the vulnerability.

How severe is CVE-2021-41258?

CVE-2021-41258 has a CVSS score of 5.4/10 (MEDIUM severity). The EPSS model estimates a 0.78% probability of exploitation in the next 30 days.

How do I fix CVE-2021-41258?

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.