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:
- Setting a crafted
x-sendfile-type: x-accel-redirect header.
- Setting a crafted
x-accel-mapping header.
- 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 body responding to
.to_path.
Mitigation
-
Upgrade to a fixed version of Rack which requires explicit configuration to enable x-accel-redirect:
use Rack::Sendfile, "x-accel-redirect"
-
Alternatively, configure the proxy to always set or strip the headers (you should be doing this!):
proxy_set_header x-sendfile-type x-accel-redirect;
proxy_set_header x-accel-mapping /var/www/=/files/;
-
Or in Rails applications, disable sendfile completely:
config.action_dispatch.x_sendfile_header = nil
References
leahneukirchen Analyst
jeremyevans Remediation reviewer
matthewd Analyst
ioquatix Remediation developer
Summary
A possible information disclosure vulnerability existed in
Rack::Sendfilewhen running behind a proxy that supportsx-sendfileheaders (such as Nginx). Specially crafted headers could causeRack::Sendfileto miscommunicate with the proxy and trigger unintended internal requests, potentially bypassing proxy-level access restrictions.Details
When
Rack::Sendfilereceived untrustedx-sendfile-typeorx-accel-mappingheaders 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:
x-sendfile-type: x-accel-redirectheader.x-accel-mappingheader.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:
Rack::Sendfilewith a proxy that supportsx-accel-redirect(e.g., Nginx).x-sendfile-typeandx-accel-mappingheaders..to_path.Mitigation
Upgrade to a fixed version of Rack which requires explicit configuration to enable
x-accel-redirect:Alternatively, configure the proxy to always set or strip the headers (you should be doing this!):
Or in Rails applications, disable sendfile completely:
References