CVE-2025-3841 Overview
A Server-Side Template Injection (SSTI) vulnerability has been identified in wix-incubator jam, affecting the Jinja2 Template Handler component within jam.py. The vulnerability arises from improper neutralization of special elements used in the template engine when processing the config['template'] argument. An attacker with local access can manipulate template parameters to inject malicious template directives, potentially leading to unauthorized code execution or information disclosure within the application context.
Critical Impact
Local attackers can exploit improper input sanitization in the Jinja2 template handler to inject malicious template code, potentially compromising application integrity.
Affected Products
- wix-incubator jam (all versions up to commit e87a6fd85cf8fb5ff37b62b2d68f917219d07ae9)
Discovery Timeline
- 2025-04-21 - CVE-2025-3841 published to NVD
- 2025-06-23 - Last updated in NVD database
Technical Details for CVE-2025-3841
Vulnerability Analysis
This vulnerability is classified as Server-Side Template Injection (CWE-94: Improper Control of Generation of Code) and relates to incomplete filtering of special elements (CWE-791). The flaw exists in the jam.py file, specifically within the Jinja2 Template Handler component. When the application processes user-controlled input through the config['template'] argument without proper sanitization, it fails to neutralize special Jinja2 template syntax elements.
Jinja2 is a powerful templating engine commonly used in Python applications. When template expressions are not properly sanitized, attackers can inject template directives that the engine will interpret and execute. This can lead to various security impacts depending on the application context, including data manipulation and potential code execution.
Root Cause
The root cause stems from insufficient input validation and sanitization of the config['template'] parameter before it is passed to the Jinja2 template engine. The application fails to properly escape or filter special template syntax characters and expressions (such as {{ }}, {% %}, and {# #}), allowing injected template code to be interpreted as legitimate template directives rather than literal strings.
Attack Vector
The attack requires local access to the system where the vulnerable application is running. An attacker with valid local credentials or access to the application's configuration interface can manipulate the template parameter to inject malicious Jinja2 expressions. Since wix-incubator jam uses a rolling release model, specific vulnerable version numbers are not available, making it essential to ensure the latest code is deployed.
The vulnerability has been publicly disclosed through a GitHub Issue Report, and additional technical details are documented in VulDB.
Detection Methods for CVE-2025-3841
Indicators of Compromise
- Unusual Jinja2 template syntax appearing in configuration files or application logs (e.g., {{ }}, {% %} patterns in unexpected locations)
- Unexpected template rendering errors or exceptions in application logs related to jam.py
- Evidence of local user accounts accessing or modifying template configuration parameters
- Anomalous process behavior or file system access following template processing operations
Detection Strategies
- Implement application-level logging to capture and monitor all template parameter inputs before processing
- Deploy file integrity monitoring on configuration files that contain template definitions
- Configure SIEM rules to alert on suspicious Jinja2 syntax patterns in log entries or input streams
- Review application audit logs for unauthorized modifications to template configurations
Monitoring Recommendations
- Monitor the jam.py component for unusual execution patterns or unexpected subprocess spawning
- Establish baseline behavior for template processing and alert on deviations
- Track local user activity and privilege usage patterns on systems running the vulnerable application
- Implement real-time alerting for configuration changes to template-related settings
How to Mitigate CVE-2025-3841
Immediate Actions Required
- Update wix-incubator jam to the latest available version from the official repository
- Review and audit all template configurations for evidence of injection attempts
- Restrict local access to systems running the affected application to trusted users only
- Implement input validation for template parameters as a defense-in-depth measure
Patch Information
The wix-incubator jam project follows a rolling release model, meaning specific version numbers for patched releases are not available. Organizations should update to the latest commit from the official GitHub repository and monitor the GitHub Issue Report for remediation guidance and patch status updates.
Workarounds
- Enable Jinja2 sandbox mode if supported by the application to restrict template execution capabilities
- Implement strict input validation to filter or escape Jinja2 special characters from user-controlled template inputs
- Restrict local system access and enforce the principle of least privilege for users who interact with the application
- Consider using Jinja2's autoescape functionality and implementing custom template filters to sanitize inputs
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
