GHSA-whrj-4476-wvmp

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::Directory prefixes 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.

HackerOne profile: https://hackerone.com/thesmartshadow

GitHub account owner: Ali Firas (@thesmartshadow)

Database specific

{
    "nvd_published_at": "2026-02-18T20:18:36Z",
    "github_reviewed_at": "2026-02-17T18:46:35Z",
    "cwe_ids": [
        "CWE-79"
    ],
    "severity": "MODERATE",
    "github_reviewed": true
}

References

Affected packages

RubyGems / rack

Package

Name: rack
Purl: pkg:gem/rack

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0Unknown introduced version / All previous versions are affected

Fixed

2.2.22

Affected versions

0.*

0.1.0

0.2.0

0.3.0

0.4.0

0.9.0

0.9.1

1.*

1.0.0

1.0.1

1.1.0

1.1.1.pre

1.1.1

1.1.2

1.1.3

1.1.4

1.1.5

1.1.6

1.2.0

1.2.1

1.2.2

1.2.3

1.2.4

1.2.5

1.2.6

1.2.7

1.2.8

1.3.0.beta

1.3.0.beta2

1.3.0

1.3.1

1.3.2

1.3.3

1.3.4

1.3.5

1.3.6

1.3.7

1.3.8

1.3.9

1.3.10

1.4.0

1.4.1

1.4.2

1.4.3

1.4.4

1.4.5

1.4.6

1.4.7

1.5.0.beta.1

1.5.0.beta.2

1.5.0

1.5.1

1.5.2

1.5.3

1.5.4

1.5.5

1.6.0.beta

1.6.0.beta2

1.6.0

1.6.1

1.6.2

1.6.3

1.6.4

1.6.5

1.6.6

1.6.7

1.6.8

1.6.9

1.6.10

1.6.11

1.6.12

1.6.13

2.*

2.0.0.alpha

2.0.0.rc1

2.0.1

2.0.2

2.0.3

2.0.4

2.0.5

2.0.6

2.0.7

2.0.8

2.0.9

2.0.9.1

2.0.9.2

2.0.9.3

2.0.9.4

2.1.0

2.1.1

2.1.2

2.1.3

2.1.4

2.1.4.1

2.1.4.2

2.1.4.3

2.1.4.4

2.2.0

2.2.1

2.2.2

2.2.3

2.2.3.1

2.2.4

2.2.5

2.2.6

2.2.6.1

2.2.6.2

2.2.6.3

2.2.6.4

2.2.7

2.2.8

2.2.8.1

2.2.9

2.2.10

2.2.11

2.2.12

2.2.13

2.2.14

2.2.15

2.2.16

2.2.17

2.2.18

2.2.19

2.2.20

2.2.21

Database specific

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/02/GHSA-whrj-4476-wvmp/GHSA-whrj-4476-wvmp.json"

RubyGems / rack

Package

Name: rack
Purl: pkg:gem/rack

Affected ranges

Type: ECOSYSTEM
Events: Introduced

3.0.0.beta1

Fixed

3.1.20

Affected versions

3.*

3.0.0.beta1

3.0.0.rc1

3.0.0

3.0.1

3.0.2

3.0.3

3.0.4

3.0.4.1

3.0.4.2

3.0.5

3.0.6

3.0.6.1

3.0.7

3.0.8

3.0.9

3.0.9.1

3.0.10

3.0.11

3.0.12

3.0.13

3.0.14

3.0.15

3.0.16

3.0.17

3.0.18

3.1.0

3.1.1

3.1.2

3.1.3

3.1.4

3.1.5

3.1.6

3.1.7

3.1.8

3.1.9

3.1.10

3.1.11

3.1.12

3.1.13

3.1.14

3.1.15

3.1.16

3.1.17

3.1.18

3.1.19

Database specific

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/02/GHSA-whrj-4476-wvmp/GHSA-whrj-4476-wvmp.json"

RubyGems / rack

Package

Name: rack
Purl: pkg:gem/rack

Affected ranges

Type: ECOSYSTEM
Events: Introduced

3.2.0

Fixed

3.2.5

Affected versions

3.*

3.2.0

3.2.1

3.2.2

3.2.3

3.2.4

Database specific

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/02/GHSA-whrj-4476-wvmp/GHSA-whrj-4476-wvmp.json"