Security release
This security release fixes two cross-site scripting (XSS) vulnerabilities from writer field and image block content printed in the site frontend.
Severity: medium (CVSS score 5.4)
Writer field
Impact
Kirby's writer field stores its formatted content as HTML code. Unlike with other field types, it is not possible to escape HTML special characters against cross-site scripting (XSS) attacks, otherwise the formatting would be lost.
Cross-site scripting (XSS) is a type of vulnerability that allows to execute any kind of JavaScript code inside the site frontend or Panel session of other users. If the user is logged in to the Panel, a harmful script can for example trigger requests to Kirby's API with the permissions of the victim.
Because the writer field did not securely sanitize its contents on save, it was possible to inject malicious HTML code into the content file by sending it to Kirby's API directly without using the Panel. This malicious HTML code 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.
This vulnerability is critical if you might have potential attackers in your group of authenticated Panel users. 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.
You are not affected if you don't use the writer field in any of your blueprints. The attack can only be performed by logged-in users and only surfaces in the site frontend (i.e. in your templates). The Panel itself is unaffected and will not execute JavaScript that was injected into writer field content.
Patches
We have patched the vulnerability in this release by sanitizing all writer field contents on the backend whenever the content is modified via Kirby's API. Please update to this or a later version (including Kirby 3.6.0) to fix the vulnerability.
More information
You can find more details like the CVE ID of this vulnerability on its security advisory page.
Image block
Impact
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 against cross-site scripting (XSS) attacks.
Cross-site scripting (XSS) is a type of vulnerability that allows to execute any kind of JavaScript code inside the site frontend or Panel session of other users. If the user is logged in to the Panel, a harmful script can for example trigger requests to Kirby's API with the permissions of the victim.
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.
This vulnerability is critical if you might have potential attackers in your group of authenticated Panel users. 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.
You are not affected if you don't use the blocks field or specifically the image block in any of your blueprints. You are also protected if you use a custom block snippet that either escapes the printed values or doesn't use them. The attack can only be performed by logged-in users and only surfaces in the site frontend (i.e. in your templates). The Panel itself is unaffected and will not execute JavaScript that was injected into the image block content.
Patches
We have patched the vulnerability in this release by escaping special HTML characters in the output from the default image block snippet. Please update to this or a later version (including Kirby 3.6.0) to fix the vulnerability.
More information
You can find more details like the CVE ID of this vulnerability on its security advisory page.
Credits
Thanks to Azrul Ikhwan Zulkifli (@azrultech) from BAE Systems AI Vulnerability Research Team for responsibly reporting the identified issues.