What’s Vulnerable › Vulnerabilities
CVE-2021-28834
- Severity: critical (CVSS 9.8 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 2.7% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2021-03-19 · updated 2026-06-17
Description
Kramdown before 2.3.1 does not restrict Rouge formatters to the Rouge::Formatters namespace, and thus arbitrary classes can be instantiated.
Affected products
- Debian Linux: 10.0
- Fedoraproject Fedora: 32, 33, 34
- Kramdown Project Kramdown: before 2.3.1 — fixed in 2.3.1
How to fix
Upgrade to a fixed version: Kramdown Project Kramdown 2.3.1. Check the vendor advisory for mitigations.
References
- https://github.com/gettalong/kramdown/compare/REL_2_3_0...REL_2_3_1
- https://github.com/gettalong/kramdown/pull/708
- https://gitlab.com/gitlab-org/gitlab/-/commit/179329b5c3c118924fb242dc449d06b4ed6ccb66
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NJCJVYHPY6LNUFM6LYZIAUIYOMVT5QGV/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/S3BBLUIDCUUR3NEE4NJLOCCAV3ALQ3O6/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SYOLQKFL6IJCQLBXV34Z4TI4O54GESPR/
- https://www.debian.org/security/2021/dsa-4890
- https://github.com/gettalong/kramdown/compare/REL_2_3_0...REL_2_3_1
- https://github.com/gettalong/kramdown/pull/708
- https://gitlab.com/gitlab-org/gitlab/-/commit/179329b5c3c118924fb242dc449d06b4ed6ccb66
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NJCJVYHPY6LNUFM6LYZIAUIYOMVT5QGV/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/S3BBLUIDCUUR3NEE4NJLOCCAV3ALQ3O6/
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