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Field injection in the KirbyData text storage handler

High
bastianallgeier published GHSA-x5mr-p6v4-wp93 Jul 27, 2023

Package

composer getkirby/cms (Composer)

Affected versions

<=3.5.8.2, 3.6.0-3.6.6.2, 3.7.0-3.7.5.1, 3.8.0-3.8.4, 3.9.0-3.9.5

Patched versions

3.5.8.3, 3.6.6.3, 3.7.5.2, 3.8.4.1, 3.9.6

Description

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, 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 during the read process the BOM was removed, turning the malicious line into a valid separator. This 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.

Patches

The problem has been patched in Kirby 3.5.8.3, Kirby 3.6.6.3, Kirby 3.7.5.2, Kirby 3.8.4.1 and Kirby 3.9.6. Please update to one of these or a later version to fix the vulnerability.

In all of the mentioned releases, we 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.

Credits

Thanks to Patrick Falb (@dapatrese) at FORMER 03 for responsibly reporting the identified issue.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L

CVE ID

CVE-2023-38488

Weaknesses

Credits