CVE-2021-29460: Kirby is an open source CMS. An editor with write access to the Kirby Panel can upload an SVG file that contains harmful content like `<script>` tags....

Description

Kirby is an open source CMS. An editor with write access to the Kirby Panel can upload an SVG file that contains harmful content like `<script>` tags. The direct link to that file can be sent to other users or visitors of the site. If the victim opens that link in a browser where they are logged in to Kirby, the script will run and can for example trigger requests to Kirby's API with the permissions of the victim. This vulnerability is critical if you might have potential attackers in your group of authenticated Panel users, as they can escalate their privileges if they get access to the Panel session of an admin user. Depending on your site, other JavaScript-powered attacks are possible. Visitors without Panel access can only use this attack vector if your site allows SVG file uploads in frontend forms and you don't already sanitize uploaded SVG files. The problem has been patched in Kirby 3.5.4. Please update to this or a later version to fix the vulnerability. Frontend upload forms need to be patched separately depending on how they store the uploaded file(s). If you use `File::create()`, you are protected by updating to 3.5.4+. As a work around you can disable the upload of SVG files in your file blueprints.

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

3.17%

86.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-79

Affected Software

Vendor	Product	Versions
Getkirby	Kirby	< 3.5.4

References

http://packetstormsecurity.com/files/162359/Kirby-CMS-3.5.3.1-Cross-Site-Scripting.htmlExploit, Third Party Advisory, VDB Entry
https://github.com/getkirby/kirby/releases/tag/3.5.4Release Notes, Third Party Advisory
https://github.com/getkirby/kirby/security/advisories/GHSA-qgp4-5qx6-548gExploit, Third Party Advisory
http://packetstormsecurity.com/files/162359/Kirby-CMS-3.5.3.1-Cross-Site-Scripting.htmlExploit, Third Party Advisory, VDB Entry
https://github.com/getkirby/kirby/releases/tag/3.5.4Release Notes, Third Party Advisory
https://github.com/getkirby/kirby/security/advisories/GHSA-qgp4-5qx6-548gExploit, Third Party Advisory

Timeline

Published: Apr 27, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-29460?

Kirby is an open source CMS. An editor with write access to the Kirby Panel can upload an SVG file that contains harmful content like `<script>` tags. The direct link to that file can be sent to other users or visitors of the site. If the victim opens that link in a browser where they are logged in to Kirby, the script will run and can for example trigger requests to Kirby's API with the permissions of the victim. This vulnerability is critical if you might have potential attackers in your group of authenticated Panel users, as they can escalate their privileges if they get access to the Panel session of an admin user. Depending on your site, other JavaScript-powered attacks are possible. Visitors without Panel access can only use this attack vector if your site allows SVG file uploads in frontend forms and you don't already sanitize uploaded SVG files. The problem has been patched in Kirby 3.5.4. Please update to this or a later version to fix the vulnerability. Frontend upload forms need to be patched separately depending on how they store the uploaded file(s). If you use `File::create()`, you are protected by updating to 3.5.4+. As a work around you can disable the upload of SVG files in your file blueprints.

How severe is CVE-2021-29460?

CVE-2021-29460 has a CVSS score of 5.4/10 (MEDIUM severity). The EPSS model estimates a 3.17% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29460?

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.