CVE Vulnerabilities

CVE-2021-32807

Improperly Controlled Modification of Dynamically-Determined Object Attributes

Published: Jul 30, 2021 | Modified: Nov 21, 2024
CVSS 3.x
7.2
HIGH
Source:
NVD
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
CVSS 2.x
6.5 MEDIUM
AV:N/AC:L/Au:S/C:P/I:P/A:P
RedHat/V2
RedHat/V3
Ubuntu

The module AccessControl defines security policies for Python code used in restricted code within Zope applications. Restricted code is any code that resides in Zopes object database, such as the contents of Script (Python) objects. The policies defined in AccessControl severely restrict access to Python modules and only exempt a few that are deemed safe, such as Pythons string module. However, full access to the string module also allows access to the class Formatter, which can be overridden and extended within Script (Python) in a way that provides access to other unsafe Python libraries. Those unsafe Python libraries can be used for remote code execution. By default, you need to have the admin-level Zope Manager role to add or edit Script (Python) objects through the web. Only sites that allow untrusted users to add/edit these scripts through the web - which would be a very unusual configuration to begin with - are at risk. The problem has been fixed in AccessControl 4.3 and 5.2. Only AccessControl versions 4 and 5 are vulnerable, and only on Python 3, not Python 2.7. As a workaround, a site administrator can restrict adding/editing Script (Python) objects through the web using the standard Zope user/role permission mechanisms. Untrusted users should not be assigned the Zope Manager role and adding/editing these scripts through the web should be restricted to trusted users only. This is the default configuration in Zope.

Weakness

The product receives input from an upstream component that specifies multiple attributes, properties, or fields that are to be initialized or updated in an object, but it does not properly control which attributes can be modified.

Affected Software

Name Vendor Start Version End Version
Accesscontrol Zope 4.0 (including) 4.3 (excluding)
Accesscontrol Zope 5.0 (including) 5.2 (excluding)

Extended Description

If the object contains attributes that were only intended for internal use, then their unexpected modification could lead to a vulnerability. This weakness is sometimes known by the language-specific mechanisms that make it possible, such as mass assignment, autobinding, or object injection.

Potential Mitigations

  • If available, use features of the language or framework that allow specification of allowlists of attributes or fields that are allowed to be modified. If possible, prefer allowlists over denylists.
  • For applications written with Ruby on Rails, use the attr_accessible (allowlist) or attr_protected (denylist) macros in each class that may be used in mass assignment.

References