CVE-2026-34230
Description
Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Utils.select_best_encoding processes Accept-Encoding values with quadratic time complexity when the header contains many wildcard (*) entries. Because this method is used by Rack::Deflater to choose a response encoding, an unauthenticated attacker can send a single request with a crafted Accept-Encoding header and cause disproportionate CPU consumption on the compression middleware path. This results in a denial of service condition for applications using Rack::Deflater. 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 |
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