CVE-2026-34826: Rack

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Utils.get_byte_ranges parses the HTTP Range header without limiting the number of individual byte ranges. Although the existing fix for CVE-2024-26141 rejects ranges whose total byte coverage exceeds the file size, it does not restrict the count of ranges. An attacker can supply many small overlapping ranges such as 0-0,0-0,0-0,... to trigger disproportionate CPU, memory, I/O, and bandwidth consumption per request. This results in a denial of service condition in Rack file-serving paths that process multipart byte range responses. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

Affected products

• Rack Rack: before 2.2.23 (fixed in 2.2.23); from 3.0.0, before 3.1.21 (fixed in 3.1.21); from 3.2.0, before 3.2.6 (fixed in 3.2.6)

Published 2026-04-02. Last modified 2026-07-24.