CVE-2025-61780
Rack is a modular Ruby web server interface. Prior to versions 2.2.20, 3.1.18, and 3.2.3, 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. 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, and requesting a path that qualifies for proxy-based acceleration. 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; and the application exposed an endpoint that returned a body responding to .to_path. Users should upgrade to Rack versions 2.2.20, 3.1.18, or 3.2.3, which require explicit configuration to enable x-accel-redirect. Alternatively, configure the proxy to always set or strip the header, or in Rails applications, disable sendfile completely.
| Software | From | Fixed in |
|---|---|---|
rack
|
- | 2.2.20 |
|
rack
|
3.0 | 3.1.18 |
|
rack
|
3.2 | 3.2.3 |
| rack / rack | - | 2.2.20 |
| rack / rack | 3.0.0 | 3.1.18 |
| rack / rack | 3.2.0 | 3.2.3 |
- https://github.com/rack/rack/commit/57277b7741581fa827472c5c666f6e6a33abd784
- https://github.com/rack/rack/commit/7e69f65eefe9cd2868df9f9f3b0977b86f93523a
- https://github.com/rack/rack/commit/fba2c8bc63eb787ff4b19bc612d315fda6126d85
- https://github.com/rack/rack/security/advisories/GHSA-r657-rxjc-j557
- https://github.com/rubysec/ruby-advisory-db/blob/master/gems/rack/CVE-2025-61780.yml
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A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
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