Plack::Middleware::XSendfile versions through 1.0053 for Perl can allow client-controlled path rewriting.
Plack::Middleware::XSendfile allows the variation setting (sendfile type) to be set by the client via the X-Sendfile-Type header, if it is not considered in the middleware constructor or the Plack environment.
A malicious client can set the X-Sendfile-Type header to "X-Accel-Redirect" to services running behind nginx reverse proxies, and then set the X-Accel-Mapping to map the path to an arbitrary file on the server.
Since 1.0053, Plack::Middleware::XSendfile is deprecated and will be removed from future releases of Plack.
This is similar to CVE-2025-61780 for Rack::Sendfile, although Plack::Middleware::XSendfile has some mitigations that disallow regular expressions to be used in the mapping, and only apply the mapping for the "X-Accel-Redirect" type.
Users can configure the X-Sendfile-Type in the middleware constructor, and the reverse proxy to unset the X-Sendfile-Type header and (on nginx) the X-Accel-Mapping request header.
Users are encouraged to set the appropriate header directly in their applications, or write their own middleware layer that does not allow configuration to be passed via HTTP request headers.