CVE-2026-34786
MediumCVSS 5.3Exploitation Probability (EPSS)
Low risk9th percentile - higher than 9% of all known CVEs
Summary
Rack::Static incorrectly evaluates header rules on the raw URL-encoded PATH_INFO, while the file is served after decoding. A request for an encoded variant of a path can bypass the intended security headers.
Risk Assessment
An attacker can bypass security headers (e.g., CSP, HSTS) attached by Rack::Static to static content, potentially facilitating XSS or other attacks.
Recommendation
Update Rack to version 2.2.23, 3.1.21, or 3.2.6, depending on the branch used.
Original NVD description (English source)
Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, 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 security-relevant response headers to static content, this can allow an attacker to bypass those headers by requesting an encoded form of the path. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.