CVE-2019-8341 in Jinja2
Summary
by MITRE
An issue was discovered in Jinja2 2.10. The from_string function is prone to Server Side Template Injection (SSTI) where it takes the "source" parameter as a template object, renders it, and then returns it. The attacker can exploit it with {{INJECTION COMMANDS}} in a URI.
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Analysis
by VulDB Data Team • 09/27/2025
The vulnerability identified as CVE-2019-8341 represents a critical Server Side Template Injection flaw within the Jinja2 template engine version 2.10. This issue stems from the unsafe handling of template source code through the from_string function, which processes user-supplied input without adequate sanitization or validation. The vulnerability manifests when applications utilize Jinja2's template rendering capabilities and accept untrusted input through the source parameter, creating an attack surface where malicious template code can be executed on the server side. The flaw directly enables attackers to inject arbitrary template commands that get processed and executed by the Jinja2 engine, potentially leading to complete system compromise.
The technical exploitation of this vulnerability occurs through the from_string function's handling of the source parameter, which accepts raw template content from external sources. When an attacker crafts malicious input containing template injection commands such as {{INJECTION COMMANDS}} within a URI, the Jinja2 engine processes this content as legitimate template syntax rather than treating it as malicious input. This processing allows the attacker to execute arbitrary code on the server, potentially accessing sensitive system resources, reading files, executing shell commands, or even establishing reverse shells. The vulnerability operates at the core of template engine security, where the boundary between user input and template execution becomes blurred due to insufficient input validation and sanitization mechanisms.
From an operational perspective, the impact of CVE-2019-8341 extends beyond simple code execution to encompass complete system compromise and data exfiltration capabilities. Attackers can leverage this vulnerability to escalate privileges, access database contents, steal session cookies, or deploy additional malware. The vulnerability affects any application using Jinja2 2.10 that accepts user input through the from_string function, making it particularly dangerous in web applications, content management systems, and any platform relying on dynamic template rendering. The attack vector through URI parameters means that even simple web requests can trigger the vulnerability, making it difficult to detect and prevent through traditional network monitoring approaches. This vulnerability aligns with CWE-94, which specifically addresses "Improper Control of Generation of Code ('Code Injection')" and follows patterns consistent with ATT&CK technique T1059.001 for command and scripting interpreter.
Organizations should implement immediate mitigations including upgrading to Jinja2 versions where this vulnerability has been patched, typically versions 2.10.1 and later. Additionally, comprehensive input validation and sanitization should be enforced for any template source parameter, with strict filtering of template syntax characters and keywords. Implementing proper template sandboxing mechanisms and restricting template execution to trusted sources only can significantly reduce the attack surface. Network segmentation and monitoring should be enhanced to detect suspicious template injection patterns, particularly in URI parameters. Security teams should also conduct thorough code reviews to identify all instances where from_string function is used with user-supplied input, ensuring that proper security controls are in place before any application deployment occurs.