Rack has a Possible Information Disclosure Vulnerability
Date: 2025-10
Affected: rubygems/rack, rubygems/rack, rubygems/rack
Attack vector: path-traversal
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2025-61780
CWE: CWE-200
CWE-441
CWE-913
CVSS: 5.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N)

## Summary A possible information disclosure vulnerability existed in `Rack::Sendfile` when running behind a proxy that supports `x-sendfile` headers (such as Nginx). Specially crafted headers could cause `Rack::Sendfile` to miscommunicate with the proxy and trigger unintended internal requests, potentially bypassing proxy-level access restrictions. ## Details When `Rack::Sendfile` received untrusted `x-sendfile-type` or `x-accel-mapping` headers from a client, it would interpret them as proxy configuration directives. This could cause the middleware to send a "redirect" response to the proxy, prompting it to reissue a new internal request that was **not subject to the proxy's access controls**. An attacker could exploit this by: 1. Setting a crafted `x-sendfile-type: x-accel-redirect` header. 2. Setting a crafted `x-accel-mapping` header. 3. Requesting a path that qualifies for proxy-based acceleration. ## Impact Attackers could bypass proxy-enforced restrictions and access internal endpoints intended to be protected (such as administrative pages). The vulnerability did not allow arbitrary file reads but could expose sensitive application routes. This issue only affected systems meeting all of the following conditions: * The application used `Rack::Sendfile` with a proxy that supports `x-accel-redirect` (e.g., Nginx). * The proxy did **not** always set or remove the `x-sendfile-type` and `x-accel-mapping` headers. * The application exposed an endpoint that returned a


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