vulnerabilities-workflow-1.md

Vulnerability List

The following vulnerability was identified in the project:

• Vulnerability Name: Cross‐Site Scripting (XSS) via Unsanitized Diff Output

  • Description: The diff generation functions (both for unified and context formats) embed user‐supplied strings into the output without applying any sanitization or escaping. An external attacker who is able to supply or influence values for fields such as the diff header file names (e.g. FromFile, ToFile) or even the diff content itself (e.g. lines from sequence A or B) may inject malicious HTML/JavaScript code. When the diff output is rendered in a web context (for example, in a publicly available web service that uses go‐difflib to show code differences), the injected payload will be executed in the victim’s browser.

    Step by step how an attacker can trigger this vulnerability:

    1. The attacker crafts a malicious payload by setting one or more of the diff header fields (for example, supplying <script>alert('XSS')</script> as the value for FromFile or ToFile).
    2. The attacker submits a request or otherwise causes the application to call the diff generation functions (such as GetUnifiedDiffString or GetContextDiffString) with the malicious header values and/or diff content.
    3. The library generates diff output by directly embedding these unsanitized strings (using formatted string calls like fmt.Sprintf("--- %s%s%s", diff.FromFile, fromDate, diff.Eol) in WriteUnifiedDiff and similar in WriteContextDiff).
    4. The resulting diff output is delivered and, if the application displays it in a browser without proper output encoding, the malicious payload is interpreted as executable HTML/JavaScript code, leading to a reflected (or stored) cross-site scripting attack.

  • Impact: If successfully exploited, the attacker can execute arbitrary JavaScript in the context of the user’s browser. This could lead to session hijacking, theft of credentials, forced redirection, or insertion of further malicious content into the web page—compromising the affected users’ security and the integrity of the application.

  • Vulnerability Rank: High

  • Currently Implemented Mitigations:

    • There are no implemented input validations or output encoding/escaping measures in the diff output routines.
    • In both WriteUnifiedDiff and WriteContextDiff, user-supplied strings (e.g. diff header fields) are incorporated directly into the formatted output.

  • Missing Mitigations:

    • Implement proper output encoding or escaping before embedding user-controlled strings into the diff output if it is to be rendered in an HTML or other script-enabled context.
    • Validate or sanitize inputs for header fields (and optionally diff content) so that any HTML/JavaScript code is either removed or safely encoded.
    • Consider adopting a secure-by-design templating strategy if the diff output is ever integrated with web UIs.

  • Preconditions:

    • The application must expose diff output generated by go‐difflib to end users in a context (such as an HTML page) where injected script code would be executed.
    • The attacker must be able to influence the diff data—either the header metadata (e.g. FromFile, ToFile, FromDate, ToDate) or the diff content itself—that is passed into functions like GetUnifiedDiffString or GetContextDiffString.

  • Source Code Analysis:

    • In the WriteUnifiedDiff function (lines near the top where headers are written), the code builds the header using:

      if diff.FromFile != "" || diff.ToFile != "" {
          err := wf("--- %s%s%s", diff.FromFile, fromDate, diff.Eol)
          if err != nil {
              return err
          }
          err = wf("+++ %s%s%s", diff.ToFile, toDate, diff.Eol)
          if err != nil {
              return err
          }
      }

      Here, the diff.FromFile and diff.ToFile values are inserted directly into the header output without any sanitization.
    • Similarly, WriteContextDiff writes headers with unsanitized strings using calls such as:

      wf("*** %s%s%s", diff.FromFile, fromDate, diff.Eol)
      wf("--- %s%s%s", diff.ToFile, toDate, diff.Eol)

      Since these fields are entirely under the control of the caller, an attacker who can supply malicious content will have their payload embedded directly into the diff output.
    • No encoding or filtering is performed on any of these strings, making the output unsafe if later rendered in (for example) an HTML page that does not perform its own escaping.

  • Security Test Case:

    1. Setup: Create or deploy an instance of an application that uses go‐difflib to generate and display diff output on a web page.
    2. Input: Invoke the diff generation API (such as by calling GetUnifiedDiffString) using a diff configuration where at least one header field (for example, FromFile) is set to a malicious payload like <script>alert('XSS')</script>.
    3. Execution:
       • Submit the request so that the resulting diff output is displayed on a web page.
       • Use a browser with its JavaScript console open.
    4. Verification:
       • Check whether the malicious script is executed (e.g. an alert box is shown).
       • Confirm that the output contains the unsanitized payload (you may inspect the page source or use developer tools to see the embedded HTML/JS).
    5. Result: If the payload executes, the vulnerability exists; otherwise, if output encoding or sanitization is applied, then the vulnerability is considered mitigated.