CVE-2024-27285 (yard): YARD’s default template vulnerable to Cross-site Scripting in generated frames.html

Ruby Security Advisory

### Summary

The “frames.html” file within the Yard Doc’s generated documentation
is vulnerable to Cross-Site Scripting (XSS) attacks due to inadequate
sanitization of user input within the JavaScript segment of the
“frames.erb” template file.

### Details

The vulnerability stems from mishandling user-controlled data retrieved
from the URL hash in the embedded JavaScript code within the “frames.erb”
template file. Specifically, the script lacks proper sanitization of
the hash data before utilizing it to establish the top-level window’s
location. This oversight permits an attacker to inject malicious
JavaScript payloads through carefully crafted URLs.

Snippet from “frames.erb”:
“`erb

“`

### PoC (Proof of Concept)

To exploit this vulnerability:
1. Gain access to the generated Yard Doc.
2. Locate and access the “frames.html” file.
3. Construct a URL containing the malicious payload in the hash
segment, for instance: `#!javascript:xss`

### Impact

This XSS vulnerability presents a substantial threat by enabling
an attacker to execute arbitrary JavaScript code within the user’s
session context. Potential ramifications include session hijacking,
theft of sensitive data, unauthorized access to user accounts, and
defacement of websites. Any user visiting the compromised page is
susceptible to exploitation. It is critical to promptly address
this vulnerability to mitigate potential harm to users and preserve
the application’s integrity.

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