Jinja2, Sandbox Escape, CVE-2024-22195 (Critical)

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This vulnerability arises due to an oversight in the Jinja2 sandboxed environment’s interaction with the `|attr` filter. The flaw allows an attacker who controls the content of a template to execute arbitrary Python code. The Jinja2 sandbox is designed to restrict access to unsafe Python operations, but the `|attr` filter can be exploited to bypass these restrictions. Specifically, an attacker can use the `|attr` filter to reference the `format` method of a string object, which is not properly restricted by the sandbox. This enables the execution of arbitrary code within the context of the application.
The vulnerability primarily affects applications that execute untrusted templates. If an attacker can inject or manipulate template content, they can leverage this flaw to escape the sandbox and execute malicious Python code. After the fix, the `|attr` filter no longer bypasses the environment’s attribute lookup, effectively mitigating the issue.

DailyCVE Form:

Platform: Jinja2
Version: Pre-3.1.3
Vulnerability: Sandbox Escape
Severity: Critical
Date: 2024-01-15

(End of form)

What Undercode Say:

Analytics:

  • Impact: Critical, as it allows arbitrary code execution.
  • Affected Systems: Applications using Jinja2 templates with untrusted input.
  • Exploitability: High if untrusted templates are processed.

Commands:

1. Check Jinja2 Version:

pip show Jinja2

2. Upgrade Jinja2:

pip install --upgrade Jinja2==3.1.3

Exploit Example:

from jinja2 import Template
template = Template("{{ ''.<strong>class</strong>.<strong>mro</strong>[1].<strong>subclasses</strong>()[186].<strong>init</strong>.<strong>globals</strong>['<strong>builtins</strong>']<a href="'__import__("os").system("id")'">'eval'</a> }}")
print(template.render())

Protection Steps:

  1. Upgrade: Ensure Jinja2 is updated to version 3.1.3 or later.
  2. Input Validation: Sanitize and validate all template inputs.
  3. Sandboxing: Use additional sandboxing mechanisms for untrusted templates.

References:

Code Snippet for Mitigation:

from jinja2 import Environment, StrictUndefined
env = Environment(undefined=StrictUndefined)
template = env.from_string("{{ safe_content }}")

By following these steps, you can protect your systems from this critical vulnerability.

References:

Reported By: https://github.com/advisories/GHSA-cpwx-vrp4-4pq7
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