CVE-2026-25500
ADVISORY - githubSummary
Summary
Rack::Directory generates an HTML directory index where each file entry is rendered as a clickable link. If a file exists on disk whose basename begins with the javascript: scheme (e.g. javascript:alert(1)), the generated index includes an anchor whose href attribute is exactly javascript:alert(1). Clicking this entry executes arbitrary JavaScript in the context of the hosting application.
This results in a client-side XSS condition in directory listings generated by Rack::Directory.
Details
Rack::Directory renders directory entries using an HTML row template similar to:
<a href='%s'>%s</a>
The %s placeholder is populated directly with the file’s basename. If the basename begins with javascript:, the resulting HTML contains an executable JavaScript URL:
<a href='javascript:alert(1)'>javascript:alert(1)</a>
Because the value is inserted directly into the href attribute without scheme validation or normalization, browsers interpret it as a JavaScript URI. When a user clicks the link, the JavaScript executes in the origin of the Rack application.
Impact
If Rack::Directory is used to expose filesystem contents over HTTP, an attacker who can create or upload files within that directory may introduce a malicious filename beginning with javascript:.
When a user visits the directory listing and clicks the entry, arbitrary JavaScript executes in the application's origin. Exploitation requires user interaction (clicking the malicious entry).
Mitigation
- Update to a patched version of Rack in which
Rack::Directoryprefixes generated anchors with a relative path indicator (e.g../filename). - Avoid exposing user-controlled directories via
Rack::Directory. - Apply a strict Content Security Policy (CSP) to reduce impact of potential client-side execution issues.
- Where feasible, restrict or sanitize uploaded filenames to disallow dangerous URI scheme prefixes.
Common Weakness Enumeration (CWE)
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
GitHub
2.3
CVSS SCORE
5.4medium| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| rack | gem | - | - | >=3.2.0,<3.2.5 | 3.2.5 |
| rack | gem | - | - | <2.2.22 | 2.2.22 |
| rack | gem | - | - | >=3.0.0.beta1,<3.1.20 | 3.1.20 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.
The attacker requires privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited. For example, a successful exploit may only be possible during the installation of an application by a system administrator.
An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
There is no impact to availability within the impacted component.