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Remote code execution (RCE) from PHP Phar archives uploaded by Panel users as content files

Critical
bastianallgeier published GHSA-g3h8-cg9x-47qw Dec 2, 2020

Package

composer getkirby/panel, getkirby/cms (Composer)

Affected versions

<=2.5.13, 3.0.0-3.4.4

Patched versions

2.5.14, 3.4.5

Description

Impact

An editor with full access to the Kirby Panel can upload a PHP .phar file and execute it on the server. This vulnerability is critical if you might have potential attackers in your group of authenticated Panel users, as they can gain access to the server with such a Phar file.

Visitors without Panel access cannot use this attack vector.

Patches

The problem has been patched in Kirby 2.5.14 and Kirby 3.4.5. Please update to one of these or a later version to fix the vulnerability.

Note: Kirby 2 reaches end of life on December 31, 2020. We therefore recommend to upgrade your Kirby 2 sites to Kirby 3. If you cannot upgrade, we still recommend to update to Kirby 2.5.14.

Workarounds

Kirby 2 sites on older releases can also be patched by applying the changes from this commit.

Credits

Thanks to Thore Imhof of Accenture for reporting the problem.

Severity

Critical

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
Changed
Confidentiality
High
Integrity
High
Availability
High

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:C/C:H/I:H/A:H

CVE ID

CVE-2020-26255

Weaknesses