Headline
CVE-2023-38488: Release 3.5.8.3 · getkirby/kirby
Kirby is a content management system. A vulnerability in versions prior to 3.5.8.3, 3.6.6.3, 3.7.5.2, 3.8.4.1, and 3.9.6 affects all Kirby sites that might have potential attackers in the group of authenticated Panel users or that allow external visitors to update a Kirby content file (e.g. via a contact or comment form). Kirby sites are not affected if they don’t allow write access for untrusted users or visitors.
A field injection in a content storage implementation is a type of vulnerability that allows attackers with content write access to overwrite content fields that the site developer didn’t intend to be modified. In a Kirby site this can be used to alter site content, break site behavior or inject malicious data or code. The exact security risk depends on the field type and usage.
Kirby stores content of the site, of pages, files and users in text files by default. The text files use Kirby’s KirbyData format where each field is separated by newlines and a line with four dashes (----). When reading a KirbyData file, the affected code first removed the Unicode BOM sequence from the file contents and afterwards split the content into fields by the field separator.
When writing to a KirbyData file, field separators in field data are escaped to prevent user input from interfering with the field structure. However this escaping could be tricked by including a Unicode BOM sequence in a field separator (e.g. --\xEF\xBB\xBF--). When writing, this was not detected as a separator, but because the BOM was removed during reading, it could be abused by attackers to inject other field data into content files.
Because each field can only be defined once per content file, this vulnerability only affects fields in the content file that were defined above the vulnerable user-writable field or not at all. Fields that are defined below the vulnerable field override the injected field content and were therefore already protected.
The problem has been patched in Kirby 3.5.8.3, 3.6.6.3, 3.7.5.2, 3.8.4.1, and Kirby 3.9.6. In all of the mentioned releases, the maintainers have fixed the affected code to only remove the Unicode BOM sequence at the beginning of the file. This fixes this vulnerability both for newly written as well as for existing content files.
🚨 Security release
This release fixes several vulnerabilities that were all responsibly reported to us in June 2023:
- Insufficient Session Expiration after a password change (high severity, CVSS score 7.3)
- Field injection in the KirbyData text storage handler (high severity, CVSS score 7.1)
- XML External Entity (XXE) vulnerability in the XML data handler (medium severity, CVSS score 6.8)
- Cross-site scripting (XSS) from MIME type auto-detection of uploaded files (medium severity, CVSS score 5.7)
- Denial of service from unlimited password lengths (medium severity, CVSS score 5.3)
Thanks to Shankar Acharya (@5hank4r), Alexandre Zanni (@noraj) at ACCEIS and Patrick Falb (@dapatrese) at FORMER 03 for responsibly reporting the identified issues.
Updated default .htaccess
We have updated the .htaccess that ships with our kits to the new version 2023-07-22, which adds protection against browser MIME type detection from malicious file uploads for files that have already been copied to the media folder. We recommend to update your sites’ .htaccess or server configuration with the new changes if you might have potential attackers in your group of authenticated Panel users or if your sites allow file uploads by visitors and the file extensions of uploaded files are not limited to a fixed safe list.
You can find the changes to the .htaccess in this commit and read more about the added rules in the security guide.
Thanks to Shankar Acharya (@5hank4r) for making us aware of this potential attack vector.
Frame-blocking in the Panel
The Panel now sends the Content-Security-Policy: frame-ancestors ‘none’ header to increase the protection against clickjacking attacks. The session cookie was already set to SameSite before, so this is an additional layer of protection.
Thanks to Shankar Acharya (@5hank4r) for suggesting this security enhancement.
Security-related breaking changes
- All users are logged out from their sessions after updating to this patch release.
- The Xml data handler (e.g. Data::decode($string, ‘xml’)) and the Xml::parse() method no longer process XML external entities.
- The Panel can no longer be embedded in HTML frames.
Related news
### TL;DR This vulnerability affects all Kirby sites that might have potential attackers in the group of authenticated Panel users or that allow external visitors to update a Kirby content file (e.g. via a contact or comment form). Your Kirby sites are *not* affected if they don't allow write access for untrusted users or visitors. ---- ### Introduction A field injection in a content storage implementation is a type of vulnerability that allows attackers with content write access to overwrite content fields that the site developer didn't intend to be modified. In a Kirby site this can be used to alter site content, break site behavior or inject malicious data or code. The exact security risk depends on the field type and usage. ### Impact Kirby stores content of the site, of pages, files and users in text files by default. The text files use Kirby's KirbyData format where each field is separated by newlines and a line with four dashes (`----`). When reading a KirbyData file, t...