PlaySMS < 1.4.3 Unauthenticated Server-Side Template Injection (SSTI) Remote Code Execution Vulnerability Analysis and Mitigation Guide (CVE-2020-8644)

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2020-8644) is a critical Server-Side Template Injection (SSTI) flaw in PlaySMS, an open-source SMS gateway management platform. PlaySMS utilizes a template engine to render dynamic web content. In versions prior to 1.4.3, the application fails to properly sanitize and validate user-supplied inputs passed to core scripts such as index.php. Consequently, when an attacker inputs malicious template syntax, the template engine interprets and executes it as executable code rather than treating it as a benign string.

2. Exploitation Mechanics & Attack Scenario

An unauthenticated attacker can target the vulnerable input fields in index.php. By crafting an HTTP request containing template engine-specific syntax (such as ${...} or {{...}}) within parameters or cookies, the attacker forces the underlying template engine to parse the payload. During the rendering process, the engine executes embedded PHP functions (e.g., system(), exec(), or passthru()), allowing the attacker to run arbitrary OS commands with the privileges of the web server daemon (e.g., www-data).

3. Infrastructure & Business Impact

With a CVSS 3.1 score of 9.8 (Critical) and its inclusion in the CISA KEV (Known Exploited Vulnerabilities) catalog, this vulnerability is actively exploited in the wild. Successful exploitation allows complete takeover of the host server. This can lead to severe business impacts, including the theft of sensitive database records, unauthorized mass SMS transmissions resulting in financial loss, and lateral movement into internal corporate networks.