CVE-2020-28734

Improper Restriction of XML External Entity Reference in Plone

Plone before 5.2.3 allows XXE attacks via a feature that is explicitly only available to the Manager role.

An XML parser processes external entity references in untrusted input, causing the server to fetch internal resources or remote URLs. Typical impact: local file disclosure, server-side request forgery, or denial of service.

CVE-2020-28734 has a CVSS score of 8.8 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.2.3, 3.2.10, 4.1.6, 2.6.8, 1.6.3); upgrading removes the vulnerable code path.

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1. What is CVE-2020-28734? CVE-2020-28734 is a high-severity XML external entity injection (XXE) vulnerability in Plone (pip), affecting versions < 5.2.3. It is fixed in 5.2.3, 3.2.10, 4.1.6, 2.6.8, 1.6.3. An XML parser processes external entity references in untrusted input, causing the server to fetch internal resources or remote URLs.
2. How severe is CVE-2020-28734? CVE-2020-28734 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2020-28734?
   • Plone (pip) (versions < 5.2.3)
   • plone.app.event (pip) (versions < 3.2.10)
   • plone.app.theming (pip) (versions < 4.1.6)
   • plone.app.dexterity (pip) (versions < 2.6.8)
   • plone.supermodel (pip) (versions < 1.6.3)
4. Is there a fix for CVE-2020-28734? Yes. CVE-2020-28734 is fixed in 5.2.3, 3.2.10, 4.1.6, 2.6.8, 1.6.3. Upgrade to this version or later.
5. Is CVE-2020-28734 exploitable, and should I be worried? Whether CVE-2020-28734 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2020-28734 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2020-28734?
   • Upgrade Plone to 5.2.3 or later
   • Upgrade plone.app.event to 3.2.10 or later
   • Upgrade plone.app.theming to 4.1.6 or later
   • Upgrade plone.app.dexterity to 2.6.8 or later
   • Upgrade plone.supermodel to 1.6.3 or later

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