CVE-2020-11056 in Sprout Forms
Summary
by MITRE
In Sprout Forms before 3.9.0, there is a potential Server-Side Template Injection vulnerability when using custom fields in Notification Emails which could lead to the execution of Twig code. This has been fixed in 3.9.0.
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Analysis
by VulDB Data Team • 10/16/2020
The vulnerability identified as CVE-2020-11056 affects Sprout Forms versions prior to 3.9.0 and represents a critical server-side template injection flaw that specifically manifests when custom fields are utilized within notification emails. This issue arises from insufficient input validation and sanitization mechanisms within the form processing pipeline, creating an avenue for malicious actors to inject and execute arbitrary Twig template code. The vulnerability is particularly concerning because it operates at the server-side template engine level, where the injection can occur through user-controllable input fields that are subsequently processed within email notification templates.
The technical exploitation of this vulnerability stems from the application's failure to properly escape or sanitize user input before incorporating it into server-side template rendering contexts. When custom fields are configured within notification emails, the system processes these fields through a template engine without adequate security controls to prevent malicious code injection. This misconfiguration allows attackers to craft input data containing Twig template syntax that gets executed during the email generation process, potentially enabling arbitrary code execution on the server. The vulnerability aligns with CWE-94, which describes improper control of generation of code, specifically highlighting the danger of template injection attacks that can lead to remote code execution.
The operational impact of this vulnerability extends beyond simple data compromise, as successful exploitation could enable attackers to execute arbitrary commands on the affected server, potentially leading to complete system compromise. Attackers could leverage this vulnerability to access sensitive data, modify form configurations, escalate privileges, or establish persistent access points within the target environment. The risk is amplified by the fact that notification emails are typically triggered by legitimate form submissions, making the attack vector less detectable and more difficult to prevent through traditional network monitoring approaches. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under T1059 for command and script injection, specifically targeting server-side template engines as a method of execution.
Organizations utilizing Sprout Forms versions prior to 3.9.0 should immediately implement mitigation strategies including updating to the patched version, implementing strict input validation for all custom fields, and configuring appropriate output encoding for template contexts. Additional defensive measures include monitoring notification email generation logs for suspicious patterns, implementing web application firewalls with template injection detection capabilities, and conducting thorough security assessments of all form configurations that utilize custom fields in notification templates. The vulnerability serves as a reminder of the critical importance of proper input sanitization and template engine security in web applications, particularly when dealing with user-controllable data that flows into server-side processing contexts.