Rack:: Static header_rules bypass via URL-encoded paths — CVE-2026-34786

Summary

## Summary `Rack::Static#applicable_rules` evaluates several `header_rules` types against the raw URL-encoded `PATH_INFO`, while the underlying file-serving path is decoded before the file is served. As a result, a request for a URL-encoded variant of a static path can serve the same file without the headers that `header_rules` were intended to apply. In deployments that rely on `Rack::Static` to attach…

Product

rubygems: rack

What to do

General, cautious steps (verify details in the official source):

• Review exposure and plan remediation based on risk and environment.
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source
• CVE Record
• NVD

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