Vulnerability Description
Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6, Rack::Multipart::Parser#handle_mime_head parses quoted multipart parameters such as Content-Disposition: form-data; name="..." using repeated String#index searches combined with String#slice! prefix deletion. For escape-heavy quoted values, this causes super-linear processing. An unauthenticated attacker can send a crafted multipart/form-data request containing many parts with long backslash-escaped parameter values to trigger excessive CPU usage during multipart parsing. This results in a denial of service condition in Rack applications that accept multipart form data. This issue has been patched in versions 3.1.21 and 3.2.6.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Rack | Rack | >= 3.0.0, < 3.1.21 |
Related Weaknesses (CWE)
References
- https://github.com/rack/rack/security/advisories/GHSA-v6x5-cg8r-vv6xVendor AdvisoryMitigation
FAQ
What is CVE-2026-34827?
CVE-2026-34827 is a vulnerability with a CVSS score of 7.5 (HIGH). Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6, Rack::Multipart::Parser#handle_mime_head parses quoted multipart parameters such as ...
How severe is CVE-2026-34827?
CVE-2026-34827 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-34827?
Check the references section above for vendor advisories and patch information. Affected products include: Rack Rack.