CVE-2026-34230
MediumCVSS 5.3Exploitation Probability (EPSS)
Low risk35th percentile - higher than 35% of all known CVEs
Summary
In the Rack interface (versions before 2.2.23, 3.1.21, and 3.2.6), a DoS vulnerability exists in the Rack::Utils.select_best_encoding method. An unauthenticated attacker can send a request with a crafted Accept-Encoding header, causing excessive CPU consumption by Rack::Deflater.
Risk Assessment
The organization is at risk of a remote DoS attack that could significantly load the server, leading to slowdown or unavailability of applications using Rack::Deflater.
Recommendation
Update Rack to version 2.2.23, 3.1.21, or 3.2.6, which contain the fix.
Original NVD description (English source)
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.