CVE-2024-56201

What it actually does

This is a remote code execution weakness in the Jinja template compiler. If an application allows an untrusted user to supply both a template’s contents and its filename, a crafted filename can interact with Jinja’s compilation process in a way that results in attacker-controlled Python code execution. The issue can bypass Jinja’s sandbox because the vulnerable behavior occurs during template compilation rather than through normal sandboxed template operations. The practical impact is execution of Python code with the privileges of the application process that compiles or renders the template.

Why it matters to the business

Applications that let users upload, create, edit, or name Jinja templates may allow an attacker to run commands inside the application runtime. This can lead to service compromise, data theft, credential exposure, modification of generated content, lateral movement from the application server, and operational disruption. The CVSS score is high, but exploitation requires a specific design pattern: the attacker must control both template content and template filename. EPSS is currently low and the issue is not listed in CISA KEV, indicating no broad confirmed exploitation signal at this time; however, exposed template-authoring features should still be treated as high priority because successful exploitation can result in full application compromise.

How an attack unfolds

An attacker first identifies an application feature that accepts user-supplied Jinja templates, such as a report builder, email-template editor, theme system, document generator, workflow engine, or plugin mechanism. The attacker then confirms that the application also lets them choose or influence the stored template filename or logical template name. They submit a malicious template body together with a specially crafted filename designed to interfere with Jinja’s compiler-generated Python code or metadata. When the application compiles or renders the template, the compiler processes the attacker-controlled filename and template content, causing arbitrary Python code to execute despite sandboxing controls. The executed code runs under the application process identity and can read environment variables, access local files available to the process, call internal services, spawn commands if permitted, or establish persistence through modified templates, jobs, or application configuration.

How to fix it

Upgrade Jinja to a fixed version. For source or Git-based consumers, use commit 877f6e51be8e1765b06d911cfaa9033775f051d1 or later. For package-manager or distribution consumers, update to the vendor release that includes this fix and rebuild/redeploy dependent applications. In addition to patching, remove the vulnerable precondition wherever possible: do not allow untrusted users to control both template content and template filename; generate server-side template names; normalize and strictly validate template identifiers; reject path separators, quotes, control characters, newlines, and unusual Unicode in template names; store user-authored templates under opaque IDs; and compile/render untrusted templates in a separate locked-down process or container with minimal privileges. Do not rely on Jinja sandboxing alone for untrusted template execution, because this flaw bypasses sandbox expectations during compilation.

How to confirm the fix worked

Confirm the deployed Jinja version or source revision includes commit 877f6e51be8e1765b06d911cfaa9033775f051d1 or a vendor-patched equivalent. Check dependency manifests, lockfiles, container images, virtual environments, and SBOMs for Jinja/Jinja2 instances, including transitive dependencies bundled into applications. Verify that any feature allowing template creation does not allow user-controlled filenames or logical template names, or that names are generated server-side and validated with a restrictive allowlist. Add a regression test that attempts to compile/render a user-controlled template with a deliberately hostile filename containing quotes, newlines, path separators, and Python-like syntax, and confirm it is rejected or safely handled. After deployment, restart application processes and rebuild images to ensure the patched library is actually loaded at runtime.

Typical attack path

1. Find an application feature that accepts user-authored Jinja templates.
2. Determine whether the same feature allows the attacker to choose or influence the template filename, path, or logical template name.
3. Create a template payload and malicious filename that trigger code execution during Jinja compilation or rendering.
4. Submit or upload the crafted template through the application, API, plugin interface, admin panel, or content-management workflow.
5. Trigger rendering, preview, compilation, export, email generation, report generation, or another action that causes Jinja to compile the template.
6. Execute Python code in the context of the application process.
7. Use that access to read secrets, access databases or internal APIs, write files, run commands, or pivot further depending on runtime permissions.

How to detect it

To determine whether exploitation already occurred, review application audit logs for template creation, upload, rename, preview, compile, render, export, or email-generation events where both template content and template name were user supplied. Look for unusual template names containing quotes, newlines, backslashes, path traversal sequences, Python keywords, parentheses, semicolons, braces, or encoded control characters. Review web access logs and API gateway logs for requests to template-management endpoints followed by render, preview, export, or job-trigger endpoints. Inspect application error logs for Jinja compilation tracebacks, SyntaxError, TemplateSyntaxError, TemplateAssertionError, sandbox violations, or stack traces referencing attacker-controlled template filenames. On hosts and containers, hunt for unexpected child processes spawned by Python application workers, such as shells, curl, wget, nc, python, perl, or bash, especially around template-rendering timestamps. Review EDR telemetry for Python processes reading secrets, cloud metadata endpoints, SSH keys, service account files, application configuration, or making unusual outbound network connections. If template content is stored, search historical templates for Python introspection and command-execution patterns commonly used in Jinja exploitation. Because no public exploit pattern is provided in the input, detection should focus on anomalous template filenames, compile errors, and post-exploitation behavior from Python/Jinja-rendering processes rather than a single definitive signature.

• TemplateSyntaxError
• TemplateAssertionError
• SandboxedEnvironment
• jinja2.exceptions
• SyntaxError: invalid syntax
• unexpected char
• unexpected token
• __globals__
• __builtins__
• __subclasses__
• __mro__
• __class__
• __import__
• os.popen
• os.system
• subprocess.Popen
• subprocess.call
• subprocess.check_output
• eval(
• exec(
• open('/etc/passwd'
• /etc/passwd
• /proc/self/environ
• /proc/self/cmdline
• /root/.ssh/id_rsa
• /.aws/credentials
• curl http://
• wget http://
• bash -c
• sh -c
• nc -e
• python -c
• perl -e
• {{ config
• {{ self
• {{ cycler
• {{ joiner
• {{ namespace
• cycler.__init__.__globals__
• joiner.__init__.__globals__
• namespace.__init__.__globals__

What your security team should do

• Inventory applications, services, plugins, and internal tools that use Jinja/Jinja2, prioritizing systems with user-authored templates, report builders, email template editors, CMS/theme features, workflow engines, or document-generation capabilities.
• Patch all affected Jinja deployments to a version containing commit 877f6e51be8e1765b06d911cfaa9033775f051d1 or later, and rebuild containers or serverless artifacts that vendor Python dependencies.
• Prioritize externally reachable or multi-tenant template-authoring features even though EPSS is low and there is no KEV listing, because successful exploitation can execute code in the application runtime.
• Remove user control over template filenames; use opaque server-generated IDs and strict allowlists for template names.
• Treat Jinja sandboxing as a defense-in-depth control, not a safe boundary for arbitrary untrusted template execution.
• Run template rendering workloads with least privilege, restricted filesystem access, no unnecessary shell utilities, limited network egress, and isolated service credentials.
• Review historical template uploads, edits, preview actions, and render failures for suspicious filenames and Python execution indicators.
• Add monitoring for unexpected child processes, outbound connections, and secret-file access from Python web or worker processes that render templates.