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.
CVSS Details
- CVSS 3.1 Base Score: 7.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Debian | — | Upgrade ruby-rack | Aug 2, 2026 | Aug 2, 2026 |
| Redhat_linux | — | No solution exists | Jul 17, 2026 | Apr 2, 2026 |
| Ubuntu | — | Upgrade ruby-rackUpgrade ruby-rack (Ubuntu Pro)Upgrade librack-ruby1.9.1 (Ubuntu Pro)Upgrade librack-ruby (Ubuntu Pro)Upgrade librack-ruby1.8 (Ubuntu Pro) | Apr 20, 2026 | Apr 17, 2026 |
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