EUVD-2026-18378
GHSA-v569-hp3g-36wr
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Lifecycle Timeline
4Tags
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.
Analysis
Denial of service in Rack::Utils.select_best_encoding allows unauthenticated remote attackers to consume disproportionate CPU resources via a crafted Accept-Encoding header containing multiple wildcard entries, affecting Rack versions prior to 2.2.23, 3.1.21, and 3.2.6. The vulnerability exploits quadratic time complexity in the encoding selection algorithm used by Rack::Deflater middleware, enabling a single HTTP request to trigger sustained CPU exhaustion and application unavailability.
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