Security patch released 20210518

Hotfix to patch various vulnerabilities. This hotfix is recommended for Plone 4.3, 5.0, 5.1 and 5.2.

This is a routine patch with our standard 14 day notice period. There is no evidence that the issues fixed here are being used against any sites.

CVE numbers: CVE numbers have been assigned; see the individual pages.

Versions Affected: All supported Plone versions (4.3.20 and any earlier 4.3.x version, 5.2.4 and any earlier 5.x version).

Versions Not Affected: None.

Zope: Zope is also affected. See details below.

Nature of vulnerabilities:

The patch will address several security issues:

  • Remote Code Execution via traversal in expressions. Reported by David Miller.
  • Writing arbitrary files via docutils and Python Script. Reported by Calum Hutton.
  • Various information disclosures: mostly installation logs. Reported by Calum Hutton.
  • Stored XSS from file upload (svg, html). Reported separately by Emir Cüneyt Akkutlu and Tino Kautschke.
  • Reflected XSS in various spots. Reported by Calum Hutton.
  • XSS vulnerability in CMFDiffTool. Reported by Igor Margitich.
  • Stored XSS from user fullname. Reported by Tino Kautschke.
  • Blind SSRF via feedparser accessing an internal URL. Reported by Subodh Kumar Shree.
  • Server Side Request Forgery via event ical URL. Reported by MisakiKata and David Miller.
  • Server Side Request Forgery via lxml parser. Reported by MisakiKata and David Miller.

Thank you to all who contacted the Plone security team to report problems!

Version support: The hotfix is officially supported by the Plone security team on the following versions of Plone in accordance with the Plone version support policy: 4.3.20, 5.0.10, 5.1.7, 5.2.4. Previous versions, like 4.2, could be affected but have not been tested. On such old versions, the hotfix might have worse side effects than what it tries to fix.

The fixes included here will be incorporated into subsequent releases of Plone, so Plone 5.2.5 and greater should not require this hotfix. 

Warning: The hotfix has not been tested with Python 2.6. Originally Plone 4.3 was supported on Python 2.6, but since a few releases this is no longer the case since. It gets ever more difficult to test on Python 2.6. By now, you may have trouble installing any package with Python 2.6.

Zope support:

Zope is also affected. New versions for Zope and other packages are available. Upgrading to those is the recommended way.

If you cannot upgrade yet, you can try the Plone hotfix. It has not been tested on Zope only, but we try not to let the Plone-specific code get in the way, so it should be okay.

These vulnerabilities mentioned above are relevant for Zope:

  • Remote Code Execution via traversal in expressions via aliases.
    Fixes released in Zope 4.6 and 5.2.
  • Remote Code Execution via traversal in expressions (no aliases).
    Fixes released in Zope 4.6.1 and 5.2.1.
  • Various information disclosures.
    Fixes released in Products.PluggableAuthService 2.6.0, Products.GenericSetup 2.1.1, and Zope 4.5.5.
  • Reflected XSS in various spots.
    Fixes released in Products.CMFCore 2.5.1 and Products.PluggableAuthService 2.6.2.

The patch was released at 2021-05-18 15:00 UTC.

Installation

Full installation instructions are available on the HotFix release page.

Standard security advice

  • Make sure that the Zope/Plone service is running with minimum privileges. Ideally, the Zope and ZEO services should be able to write only to log and data directories. Plone sites installed through our installers already do this.
  • Use an intrusion detection system that monitors key system resources for unauthorized changes.
  • Monitor your Zope, reverse-proxy request and system logs for unusual activity.
  • Make sure your administrator stays up to date, by following the special low-volume Plone Security Announcements list via email, RSS and/or Twitter

These are standard precautions that should be employed on any production system, and are not tied to this fix.

Extra Help

If you do not have in-house server administrators or a service agreement for supporting your website, you can find consulting companies at plone.com/providers

There is also free support available online via the Plone forum and the Plone chat channels.

Q: When will the patch be made available?
A: The Plone Security Team released the patch at 2021-05-18 15:00 UTC.

Q. What will be involved in applying the patch?
A. Patches are made available as tarball-style archives that may be unpacked into the products folder of a buildout installation (for Plone 5.1.x and earlier only) and as Python packages that may be installed by editing a buildout configuration file and running buildout. Patching is generally easy and quick to accomplish.

Q: How were these vulnerabilities found?
A: The vulnerabilities were found by users submitting them to the security mailing list.

Q: My site is highly visible and mission-critical. I hear the patch has already been developed. Can I get the fix before the release date?
A: No. The patch will be made available to all administrators at the same time. There are no exceptions.

Q: If the patch has been developed already, why isn't it made available to the public now?
 A: The Security Team is still testing the patch against a wide variety of configurations and running various scenarios thoroughly. The team is also making sure everybody has appropriate time to plan to patch their Plone installation(s). Some consultancy organizations have hundreds of sites to patch and need the extra time to coordinate their efforts with their clients.

Q: How does one exploit the vulnerability?
A: This information will not be made public until after the patch is made available.

Q: Is my Plone site at risk for this vulnerability? How do I know if my site has been exploited? How can I confirm that the hotfix is installed correctly and my site is protected?

A: Details about the vulnerability will be revealed at the same time as the patch.

Q: How can I report other potential security vulnerabilities?

A: Please email the Plone Security Team at security@plone.org rather than publicly discussing potential security issues.

Q: How can I apply the patch without affecting my users?

A: Even though this patch does NOT require you to run buildout, you can run buildout without affecting your users. You can restart a multi-client Plone install without affecting your users; see http://docs.plone.org/manage/deploying/processes.html  

Q: How do I get help patching my site?

A: Plone service providers are listed at plone.com/providers  There is also free support available online via the Plone forum and the Plone chat channels

Q: Who is on the Plone Security Team and how is it funded?

A: The Plone Security Team is made up of volunteers who are experienced developers familiar with the Plone code base and with security exploits. The Plone Security Team is not funded; members and/or their employers have volunteered their time in the interests of the greater Plone community.

Q: How can I help the Plone Security Team?

A: The Plone Security Team is looking for help from security-minded developers and testers. Volunteers must be known to the Security Team and have been part of the Plone community for some time. To help the Security Team financially, your donations are most welcome at http://plone.org/sponsors

General questions about this announcement, Plone patching procedures, and availability of support may be addressed to the Plone support forums If you have specific questions about this vulnerability or its handling, contact the Plone Security Team at security@plone.org

To report potentially security-related issues, email the Plone Security Team at security@plone.org We are always happy to credit individuals and companies who make responsible disclosures.

Information for Vulnerability Database Maintainers

We will apply for CVE numbers for these issues. Further information on individual vulnerabilities (including CVSS scores, CWE identifiers and summaries) will be available at the full vulnerability list.