CVE-2026-34230 — Rack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encoding header

Description (CNA)

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.

Affected (CNA)

Vendor / product	Versions
rack / rack	affected < 2.2.23; affected >= 3.0.0.beta1, < 3.1.21; affected >= 3.2.0, < 3.2.6

CWE

CWE-400, CWE-407

References

https://github.com/rack/rack/security/advisories/GHSA-v569-hp3g-36wr

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.