CVE-2026-26961
Description
Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser extracts the boundary parameter from multipart/form-data using a greedy regular expression. When a Content-Type header contains multiple boundary parameters, Rack selects the last one rather than the first. In deployments where an upstream proxy, WAF, or intermediary interprets the first boundary parameter, this mismatch can allow an attacker to smuggle multipart content past upstream inspection and have Rack parse a different body structure than the intermediary validated. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.
How to fix
- rack rack2.2.23, 3.1.21, 3.2.6 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| rack rack | v < 2.2.23, 3.0.0 ≤ v < 3.1.21, 3.2.0 ≤ v < 3.2.6 | 2.2.23, 3.1.21, 3.2.6 |
Check your version
Choose the product and enter the version you run to see whether it falls in the affected range.
Attack Surface Management
See the assets tied to your domains, the technologies they run and known vulnerabilities in one list.