CVE-2024-45614: Puma

Medium severity, CVSS 5.4. EPSS: 0.6% chance of exploitation in the next 30 days.

Puma is a Ruby/Rack web server built for parallelism. In affected versions clients could clobber values set by intermediate proxies (such as X-Forwarded-For) by providing a underscore version of the same header (X-Forwarded_For). Any users relying on proxy set variables is affected. v6.4.3/v5.6.9 now discards any headers using underscores if the non-underscore version also exists. Effectively, allowing the proxy defined headers to always win. Users are advised to upgrade. Nginx has a underscores_in_headers configuration variable to discard these headers at the proxy level as a mitigation. Any users that are implicitly trusting the proxy defined headers for security should immediately cease doing so until upgraded to the fixed versions.

Affected products

• Puma Puma: before 5.6.9 (fixed in 5.6.9); from 6.0.0, before 6.4.3 (fixed in 6.4.3)

Published 2024-09-19. Last modified 2026-06-17.