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Cross-site scripting (XSS) from content entered in the tags and multiselect fields

High
lukasbestle published GHSA-rv3r-vqjj-8c76 Aug 24, 2022

Package

composer getkirby/cms (Composer)

Affected versions

3.5.7-3.7.3

Patched versions

3.5.8.1, 3.6.6.1, 3.7.4

Description

Introduction

Cross-site scripting (XSS) is a type of vulnerability that allows to execute any kind of JavaScript code inside the Panel session of the same or 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.

Impact

The tags and multiselect fields allow to select tags from an autocompleted list. The tags field also allows to enter new tags or edit existing tags. Kirby already handled escaping of the autocompleted tags, but unfortunately the Panel used HTML rendering for new or edited tags as well as for custom tags from the content file.

This allowed attackers with Panel access to store malicious HTML code in a tag. The browser of the victim who visited the modified page in the Panel will then have rendered this malicious HTML code.

It also allowed self-inflicted XSS attacks in the tags field (meaning that malicious code is executed in the browser of the user who entered it). This could be used in social engineering attacks where a victim is convinced by an attacker to enter malicious code into a tags field.

Visitors without Panel access could only use this attack vector if your site allows changing the content of a tags or multiselect field 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.

You are also not affected by these vulnerabilities if your site doesn't have untrustworthy users with Panel access or a way to modify field values from the frontend or if you don't use the tags or multiselect fields.

Patches

The problems have been patched in Kirby 3.5.8.1, Kirby 3.6.6.1 and Kirby 3.7.4. Please update to one of these or a later version to fix the vulnerabilities.

Note: The fixes for these vulnerabilities have the side effect that values in the tags and multiselect fields that come from dynamic options are displayed with double escaping (e.g. the & character is displayed as &). In the fix for Kirby 3.5, every value in the tags field is displayed with double escaping when dynamic options are enabled, while dynamic options themselves are displayed with triple escaping. We will fix the double/triple escaping issues with a refactoring of the options fields (tags, multiselect, checkboxes, radio, select and toggles) in Kirby 3.8.

Workarounds

We recommend to update to one of the patch releases. If you cannot update immediately, you can work around the issue by disabling the tags and multiselect fields. This can be done by uncommenting these fields from all your blueprints.

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-2022-35174

Weaknesses