CVE-2021-32674

TAL expression traversal vulnerabilities in Zope

• CVSS 8.8
• CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
• Input Validation and Sanitization
• Remote

Zope is an open-source web application server. This advisory extends the previous advisory at https://github.com/zopefoundation/Zope/security/advisories/GHSA-5pr9-v234-jw36 with additional cases of TAL expression traversal vulnerabilities. Most Python modules are not available for using in TAL expressions that you can add through-the-web, for example in Zope Page Templates. This restriction avoids file system access, for example via the 'os' module. But some of the untrusted modules are available indirectly through Python modules that are available for direct use. By default, you need to have the Manager role to add or edit Zope Page Templates through the web. Only sites that allow untrusted users to add/edit Zope Page Templates through the web are at risk. The problem has been fixed in Zope 5.2.1 and 4.6.1. The workaround is the same as for https://github.com/zopefoundation/Zope/security/advisories/GHSA-5pr9-v234-jw36: A site administrator can restrict adding/editing Zope Page Templates through the web using the standard Zope user/role permission mechanisms. Untrusted users should not be assigned the Zope Manager role and adding/editing Zope Page Templates through the web should be restricted to trusted users only.

CVE

CVE-2021-32674

CWE

CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

CVSS base score

8.8

Published

2021-06-08

OWASP

A01 Broken Access Control

Orthogonal defect classification

Function

Code defect classification

Missing Functionality

Category

Input Validation and Sanitization

Subcategory

Path Traversal

Accessibility scope

Remote

Impact

Arbitrary Code Execution

Fixed by upgrading

Yes

Solution

Update Zope to version 5.2.1 or 4.6.1.

from Products.PageTemplates.PageTemplateFile import PageTemplateFile

class ModifiedPageTemplate(PageTemplateFile):
    def __init__(self, id, text, **kwargs):
        super().__init__(id, text, **kwargs)

    def render(self, *args, **kwargs):
        return super().render(*args, **kwargs)

from Products.PageTemplates.PageTemplateFile import PageTemplateFile
import os

class ModifiedPageTemplate(PageTemplateFile):
    def __init__(self, filename, dir_path, **kwargs):
        full_path = os.path.abspath(os.path.join(dir_path, filename))

        if not full_path.startswith(os.path.abspath(dir_path)):
            raise ValueError("Invalid template path.")

        if not os.path.isfile(full_path):
            raise FileNotFoundError("Template file does not exist.")

        super().__init__(filename, dir_path, **kwargs)

    def render(self, *args, **kwargs):
        return super().render(*args, **kwargs)

@misc{vaitp:cve202132674,
  title        = {{TAL expression traversal vulnerabilities in Zope}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2021},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2021-32674},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2021-32674/}}
}