CVE-2019-10906 in Jinja
Summary
by MITRE
In Pallets Jinja before 2.10.1, str.format_map allows a sandbox escape.
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Analysis
by VulDB Data Team • 05/20/2025
The vulnerability identified as CVE-2019-10906 affects the Jinja templating engine within the Pallets project, specifically impacting versions prior to 2.10.1. This issue represents a critical sandbox escape vulnerability that undermines the security model designed to isolate template execution from underlying system operations. The vulnerability exists within the str.format_map method implementation, which is commonly used for string formatting within template contexts. When attackers can manipulate template rendering through this method, they gain unauthorized access to system resources that should remain protected by the sandbox environment.
The technical flaw stems from insufficient validation and sanitization within the str.format_map function implementation in Jinja templates. This vulnerability allows malicious actors to bypass the intended security boundaries of the templating engine by crafting specific template inputs that exploit the method's behavior. The sandbox escape occurs because the format_map functionality does not properly restrict access to underlying object attributes or methods that could provide unauthorized system access. This weakness specifically affects how template variables are processed and formatted, creating an avenue for arbitrary code execution or information disclosure. The vulnerability is classified under CWE-20 as "Improper Input Validation" and aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter, as it enables execution of arbitrary commands through template manipulation.
The operational impact of this vulnerability is severe for applications relying on Jinja templating for user-generated content processing or dynamic template rendering. Attackers can leverage this vulnerability to execute arbitrary commands on the host system, potentially leading to complete system compromise. The vulnerability affects web applications, content management systems, and any platform that utilizes Jinja templates for dynamic content generation. Organizations using affected versions face significant risk of data breaches, system infiltration, and unauthorized access to sensitive information. The sandbox escape capability means that even if applications properly validate user input, the underlying template engine vulnerability can still be exploited to gain elevated privileges or access system resources.
Mitigation strategies for CVE-2019-10906 require immediate patching of affected Jinja installations to version 2.10.1 or later, which contains the necessary security fixes. Organizations should also implement additional defensive measures including strict input validation for all template variables, monitoring for suspicious template usage patterns, and regular security audits of template processing code. The remediation process should include comprehensive testing to ensure that the patch does not introduce regressions in existing functionality while maintaining the security improvements. Security teams should also consider implementing runtime monitoring solutions that can detect anomalous template behavior indicative of exploitation attempts. Additional protective measures include restricting template execution permissions, implementing network segmentation, and establishing incident response procedures specifically addressing template injection vulnerabilities. The fix addresses the core issue by properly validating and sanitizing template inputs before processing them through the format_map method, thereby preventing unauthorized access to system resources through the templating engine.