CVE-2021-33511: Plone Server-Side Request Forgery Vulnerability

HIGH
Advisory Identifier: GHSA-gc9g-67cq-p7v4
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CVSS 7.5
CWE-918
Published
Advisory Summary

CVE-2021-33511 is a HIGH (CVSS 7.5) server-side request forgery vulnerability (CWE-918: Server-Side Request Forgery (SSRF)) affecting Plone libraries in the PyPI ecosystem. The issue involves server-side request forgery in plone. Remediation is available in the latest vendor maintenance releases.

CVE-2021-33511 at a Glance

CVE Identifier CVE-2021-33511
GHSA Identifier GHSA-gc9g-67cq-p7v4
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-918: Server-Side Request Forgery (SSRF)
Affected Product Plone
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2021-33511

To remediate this vulnerability, upgrade all affected Plone dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Plone fixed: Latest secure release 
pip install Plone>=Latest secure release
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show Plone

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-33511, inspect your installed packages using pip:

pip show Plone

Analyze the terminal output to locate any version of Plone in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The pip show Plone command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-918: Server-Side Request Forgery (SSRF), where the web server receives a url or similar request from an upstream component and retrieves the contents of this url, but it does not sufficiently ensure that the request is being sent to the expected destination. In Plone, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Plone though 5.2.4 allows SSRF via the lxml parser. This affects Diazo themes, Dexterity TTW schemas, and modeleditors in plone.app.theming, plone.app.dexterity, and plone.supermodel.

CVE-2021-33511 Affected Plone Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
Plone
pypi/Plone
PyPI
≤ 5.2.4

References

NVD — CVE-2021-33511 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-33511
GitHub Advisory / Wiki ADVISORY
https://github.com/advisories/GHSA-gc9g-67cq-p7v4
Plone Source Repository REPOSITORY
https://github.com/plone/Plone
Plone Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/plone/PYSEC-2021-83.yaml
Plone Security Information SECURITY
https://plone.org/security/hotfix/20210518/server-side-request-forgery-via-lxml-parser
Plone Security Information SECURITY
http://www.openwall.com/lists/oss-security/2021/05/22/1

Frequently Asked Questions

What is CVE-2021-33511?
CVE-2021-33511 is a security vulnerability in Plone involving Server-Side Request Forgery in Plone under CWE-918: Server-Side Request Forgery (SSRF).
Which Plone versions are affected?
Affected versions include releases prior to current release patches across affected packages: Plone.
What version fixes CVE-2021-33511?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is Plone affected?
Yes, Plone is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2021-33511?
CVE-2021-33511 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2021-33511?
CVE-2021-33511 is classified under CWE-918: Server-Side Request Forgery (SSRF) (The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.).
How can I check PyPI dependencies for CVE-2021-33511?
Run the dependency tree command: 'pip show Plone'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-gc9g-67cq-p7v4",
  "modified" : "2024-10-18T21:48:44Z",
  "published" : "2021-06-15T16:12:04Z",
  "aliases" : [ "CVE-2021-33511" ],
  "summary" : "Server-Side Request Forgery in Plone",
  "details" : "Plone though 5.2.4 allows SSRF via the lxml parser. This affects Diazo themes, Dexterity TTW schemas, and modeleditors in plone.app.theming, plone.app.dexterity, and plone.supermodel.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "Plone"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "5.2.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-33511"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-gc9g-67cq-p7v4"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/plone/Plone"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/plone/PYSEC-2021-83.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://plone.org/security/hotfix/20210518/server-side-request-forgery-via-lxml-parser"
  }, {
    "type" : "WEB",
    "url" : "http://www.openwall.com/lists/oss-security/2021/05/22/1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-918" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-05-27T21:47:01Z",
    "nvd_published_at" : "2021-05-21T22:15:00Z"
  }
}