CVE-2026-34230
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.
- Rack
- < 2.2.23, 3.1.21, 3.2.6
- Fix
- Available
- CVSS 3.1
- 7.5 HIGH
- EPSS
- 0.4% (35th percentile)
- Weakness
- CWE-407, CWE-400
- NVD status
- Analyzed
- Published
- 2026-04-02
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