CVE-2025-61780

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.

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
  

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.

CVE-2025-61780 has a CVSS score of 5.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.2.20, 3.1.18, 3.2.3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-61780? CVE-2025-61780 is a medium-severity security vulnerability in rack (rubygems), affecting versions < 2.2.20. It is fixed in 2.2.20, 3.1.18, 3.2.3.
2. How severe is CVE-2025-61780? CVE-2025-61780 has a CVSS score of 5.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of rack are affected by CVE-2025-61780? rack (rubygems) versions < 2.2.20 is affected.
4. Is there a fix for CVE-2025-61780? Yes. CVE-2025-61780 is fixed in 2.2.20, 3.1.18, 3.2.3. Upgrade to this version or later.
5. Is CVE-2025-61780 exploitable, and should I be worried? Whether CVE-2025-61780 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-61780 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-61780?
   • Upgrade rack to 2.2.20 or later
   • Upgrade rack to 3.1.18 or later
   • Upgrade rack to 3.2.3 or later