CVE-2026-34830: Rack

High severity, CVSS 7.5. EPSS: 0.4% 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::Sendfile#map_accel_path interpolates the value of the X-Accel-Mapping request header directly into a regular expression when rewriting file paths for X-Accel-Redirect. Because the header value is not escaped, an attacker who can supply X-Accel-Mapping to the backend can inject regex metacharacters and control the generated X-Accel-Redirect response header. In deployments using Rack::Sendfile with x-accel-redirect, this can allow an attacker to cause nginx to serve unintended files from configured internal locations. 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.