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.
CVSS Details
- CVSS 3.1 Base Score: 5.4
- CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Debian | — | Upgrade puma | Nov 11, 2024 | Sep 19, 2024 |
| Suse | — | Upgrade ruby2.5-rubygem-puma-docUpgrade ruby2.5-rubygem-puma | Dec 5, 2025 | Oct 16, 2024 |
| Ubuntu | — | Upgrade puma (Ubuntu Pro)Upgrade puma | Sep 25, 2024 | Sep 19, 2024 |
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