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Cross-site scripting (XSS) from field and configuration text displayed in the Panel

High
lukasbestle published GHSA-2f2w-349x-vrqm Jul 2, 2021

Package

composer getkirby/cms (Composer)

Affected versions

<=3.5.6

Patched versions

3.5.7

Description

On Saturday, @hdodov reported that the Panel's ListItem component (used in the pages and files section for example) displayed HTML in page titles as it is. This could be used for cross-site scripting (XSS) attacks.

We used his report as an opportunity to find and fix XSS issues related to dynamic site content throughout the Panel codebase.

Impact

Cross-site scripting (XSS) is a type of vulnerability that allows to execute any kind of JavaScript code inside the Panel session of other users. In the Panel, a harmful script can for example trigger requests to Kirby's API with the permissions of the victim.

Such vulnerabilities are 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.

Visitors without Panel access can only use this attack vector if your site allows changing site data from a frontend form (for example user self-registration or the creation of pages from a contact or other frontend form). If you validate or sanitize the provided form data, you are already protected against such attacks by external visitors.

Patches

Kirby 3.5.7 contains patches for the following issues we found during our investigation:

  • Some translated error and info messages contain placeholders to dynamically insert information like page titles or filenames. While the translation strings are allowed to contain HTML formatting, the dynamic data needs to be protected against XSS attacks. Kirby 3.5.7 now escapes the dynamic data.
  • Our Box component used to display information for the user supports HTML output for specific use-cases. We found out that the dialogs used in the files, pages and users fields as well as the fields section used it to display raw exception or error messages. These messages are now escaped.
  • The users and settings views display user and language data using the ListItem component that supports HTML. We now escape the dynamic data before it is passed to the ListItem component.
  • Some of our sections and fields support HTML for their text, help and/or info properties. This allows custom formatting from the blueprint, but also caused the original issue reported to us that allowed to inject HTML code from the content itself. Kirby 3.5.7 now escapes the default text displayed by the files and pages sections (filename/page title), the files, pages and users fields (filename/page title/username) and by query-based checkboxes, radio, tags and multiselect fields (default text depending on the used query).

Note: Custom text, help and info queries in blueprints are not escaped in 3.5.7. We support HTML in these properties because there are valid use-cases for custom formatting. However there can still be XSS vulnerabilities depending on your use of these properties. In Kirby 3.6 we will provide a new feature that will make it much easier to control whether you want to allow HTML from query placeholders.

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
High
Integrity
Low
Availability
None

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:H/I:L/A:N

CVE ID

CVE-2021-32735

Weaknesses

Credits