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.
References:- https://nvd.nist.gov/vuln/detail/CVE-2021-33511
- https://plone.org/security/hotfix/20210518/server-side-request-forgery-via-lxml-parser
- http://www.openwall.com/lists/oss-security/2021/05/22/1
- https://github.com/advisories/GHSA-gc9g-67cq-p7v4
- https://github.com/pypa/advisory-database/tree/main/vulns/plone/PYSEC-2021-83.yaml