Kramdown before 2.3.1 does not restrict Rouge formatters to the Rouge::Formatters…
Priority MEDIUM 47CWE-94Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Code execution
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Fixed
Attack profile from CVSS 3.1 · NVD. Fix status from CNA and GitHub. Impact type from CWE-94.
Summary
Kramdown before 2.3.1 does not restrict Rouge formatters to the Rouge::Formatters namespace, and thus arbitrary classes can be instantiated.
Why it matters now
EPSS 0.02695 86th percentileScored 2026-11-08
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed kramdown (RubyGems): 2.3.1
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | — | all versions | — | No fix listed | CNA |
| — | kramdown (RubyGems) | 1.16.0 to before 2.3.1 | 2.3.1 | Patch available | GHSA-52p9-v744-mwjj |
- — Vendor— Affected all versions Fixed in — No fix listed CNA
- kramdown (RubyGems) Vendor— Affected 1.16.0 to before 2.3.1 Fixed in 2.3.1 Patch available GHSA-52p9-v744-mwjj
CPE configurations NVD · 5
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:kramdown_project:kramdown:*:*:*:*:*:ruby:*:* | before 2.3.1 | Vulnerable | Kramdown Project |
| cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:* | 32 | Vulnerable | Fedoraproject |
| cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:* | 33 | Vulnerable | Fedoraproject |
| cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:* | 34 | Vulnerable | Fedoraproject |
| cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* | 10.0 | Vulnerable | Debian |
- cpe:2.3:a:kramdown_project:kramdown:*:*:*:*:*:ruby:*:* Versions before 2.3.1 Vulnerable ·Kramdown Project
- cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:* Versions 32 Vulnerable ·Fedoraproject
- cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:* Versions 33 Vulnerable ·Fedoraproject
- cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:* Versions 34 Vulnerable ·Fedoraproject
- cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* Versions 10.0 Vulnerable ·Debian
Remediation
- Fix · GHSA-52p9-v744-mwjj kramdown (RubyGems) Fixed in 2.3.1 Advisory →
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2021-28834
- 2026-10-03 Alias added: GHSA-52p9-v744-mwjj
References
Patch 2
Advisory 5
Other 6
- https://github.com/stanhu/kramdown/commit/d6a1cbcb2caa2f8a70927f176070d126b2422760
- https://github.com/stanhu/kramdown/commit/ff0218aefcf00cd5a389e17e075d36cd46d011e2
- https://about.gitlab.com/releases/2021/03/17/security-release-gitlab-13-9-4-released/#remote-code-execution-via-unsafe-user-controlled-markdown-rendering-options
- https://lists.fedoraproject.org/archives/list/[email protected]/message/NJCJVYHPY6LNUFM6LYZIAUIYOMVT5QGV
- https://lists.fedoraproject.org/archives/list/[email protected]/message/S3BBLUIDCUUR3NEE4NJLOCCAV3ALQ3O6
- https://lists.fedoraproject.org/archives/list/[email protected]/message/SYOLQKFL6IJCQLBXV34Z4TI4O54GESPR
Sources
- CVE-2021-28834 · CVE Program
- CVE-2021-28834 · NVD
- FIRST EPSS
- GHSA-52p9-v744-mwjj · GitHub Advisory Database · CC BY 4.0
- CVE-2021-28834 · Red Hat security data · CC BY 4.0
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