Security readout for executives and security teams
Plain-English summary
This vulnerability lets a logged-in attacker abuse Plone CMS RSS feed portlet behavior to make the server reach internal URLs. That can expose sensitive internal information and is rated high severity. The provided sources do not show active exploitation or CISA KEV listing.
Executive priority
Treat as high priority for internet-facing or business-critical Plone sites, especially where authenticated users are numerous or loosely governed. Remediate through the vendor hotfix path and reduce internal network reachability from Plone servers.
Technical view
CVE-2021-33926 is a Plone CMS blind SSRF issue tied to feedparser handling in the RSS feed portlet. The CVSS 3.1 vector is AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H with CWE-918. Affected versions are described across Plone 4.x and 5.x releases, including 5.2.4.
Likely exposure
Exposure is most likely where Plone CMS 4.x or 5.x sites use affected RSS feed portlet/feedparser functionality and allow authenticated users to configure or influence feed URLs.
Exploitation context
The source bundle supports a network-accessible, low-complexity issue requiring low privileges and no user interaction. KEV is false, and the provided sources do not establish real-world exploitation.
Researcher notes
Evidence points to blind SSRF through feedparser accessing internal URLs via the RSS feed portlet. The provided CVE metadata lists broad Plone 4.x and 5.x versions, but the affected product fields are sparse, so validate against vendor advisories.
Mitigation direction
- Apply the Plone 20210518 security hotfix where applicable.
- Check Plone vendor guidance for supported upgrade or fixed-release options.
- Disable unneeded RSS feed portlets until remediation is confirmed.
- Restrict Plone server outbound access to sensitive internal services.
- Review internal services reachable from Plone application networks.
Validation and detection
- Inventory Plone CMS versions across public and internal deployments.
- Confirm affected sites have the 20210518 hotfix or vendor-approved fix applied.
- Identify pages or roles that can configure RSS feed portlets.
- Review logs for unusual feed retrievals to internal-only addresses.
- Validate egress controls limit server-side access to internal systems.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-918: Information exposure and cloud metadata lookup
Information exposure and SSRF weaknesses can make discovery, cloud metadata, and credential material review relevant. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-33926 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H2.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.8HighVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://plone.org/security/hotfix/20210518CVE reference
- https://github.com/s-kustm/Subodh/blob/master/Plone%205.2.4%20Vulnerable%20to%20bilend%20SSRF.pdfCVE reference
- https://plone.org/security/hotfix/20210518/blind-ssrf-via-feedparser-accessing-an-internal-urlCVE reference
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Server-Side Request Forgery (SSRF)
Server-Side Request Forgery (SSRF) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.