CVE-2016-10745 in Jinja
Summary
by MITRE
In Pallets Jinja before 2.8.1, str.format allows a sandbox escape.
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Analysis
by VulDB Data Team • 08/27/2023
The vulnerability identified as CVE-2016-10745 represents a critical sandbox escape flaw within the Jinja templating engine, a widely used component in Python web applications and frameworks. This issue specifically affects versions of Pallets Jinja prior to 2.8.1, where the str.format method fails to properly isolate template execution contexts, creating a pathway for malicious code injection. The vulnerability stems from insufficient sandboxing mechanisms that should prevent template authors from accessing underlying system resources or executing arbitrary Python code through template rendering processes.
The technical flaw manifests when template developers utilize the str.format method within Jinja templates, particularly in contexts where user input is processed through template variables. The sandbox escape occurs because the format method can be manipulated to access the underlying Python object model, allowing attackers to bypass template security restrictions. This vulnerability operates under the Common Weakness Enumeration category CWE-242, which addresses "Risk of Invoking Methods on Untrusted Objects," and aligns with ATT&CK technique T1059.001 for executing code through command-line interfaces. The flaw essentially allows an attacker to escalate privileges within the template execution environment, potentially gaining access to system resources, file operations, or network capabilities that should remain restricted.
The operational impact of this vulnerability extends beyond simple code injection, as it can enable full system compromise when exploited in web applications that process untrusted user input through Jinja templates. Attackers can leverage this vulnerability to execute arbitrary commands on the server, read sensitive files, or even establish persistent backdoors within the application environment. The risk is particularly severe in applications that use Jinja for dynamic content generation, email templating, or any scenario where user-supplied data is processed through template engines. This vulnerability has been documented to affect major frameworks including Flask and other Python web applications that depend on Pallets Jinja for their templating functionality.
Mitigation strategies for CVE-2016-10745 primarily involve immediate upgrading to Pallets Jinja version 2.8.1 or later, which includes proper sandboxing controls for the str.format method. Organizations should implement comprehensive patch management procedures to ensure all affected systems are updated promptly. Additional defensive measures include strict input validation for all template variables, implementation of template access controls, and regular security auditing of template code to identify potential sandbox escape vectors. Security teams should also consider implementing runtime monitoring solutions that can detect anomalous template execution patterns indicative of exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date dependencies in web applications and highlights the necessity of robust sandboxing mechanisms in interpreted template engines. Organizations should also review their template security policies and ensure that template execution contexts are properly isolated from system-level operations to prevent similar vulnerabilities from emerging in other components of their application stack.