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The vulnerability, identified in the pretix newsletter plugin, stems from a failure to properly sanitize user-controlled input within email template placeholders. Pretix uses a templating engine that evaluates placeholders like `{name}` by replacing them with customer data. However, due to a flaw in the plugin’s input filtering, an attacker with backend access (typically any event organizer user) could inject malicious placeholders such as {{event.__init__.__code__.co_filename}}. This specific payload leverages Python’s ability to traverse object properties, allowing the attacker to escape the intended sandbox and read attributes of the `event` object. By chaining such traversals, an attacker could access the event’s configuration object, which holds the application’s settings loaded from pretix.cfg. This configuration file commonly contains highly sensitive secrets, including database passwords (e.g., database.PASSWORD) and API keys for external services. The pre-existing security mechanisms designed to block such traversal attacks were present but contained a bypass in their implementation for this specific plugin, leaving the system vulnerable to server-side template injection and subsequent information disclosure.
Platform: pretix Enterprise newsletter plugin
Version: 1.0.0 through <2.0.1
Vulnerability: Dynamic Variable Evaluation
Severity: HIGH 7.5 CVSS:4.0
date: 2026-02-16
Prediction: Already patched 2026-02-16
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The vulnerability, a Dynamic Variable Evaluation (CWE-627), is specific to the `pretix-newsletter` plugin. It is not exploitable by anonymous users; it requires an authenticated user with permissions to modify email templates (e.g., event organizers in a multi-tenant setup). The CVSS 4.0 score of 7.5 (High) reflects the Low privileges required and the High impact on confidentiality, as it allows retrieval of database passwords and API keys from the `pretix.cfg` file. The attack complexity is High, as it requires knowledge of the specific object structure to inject successfully. The vendor confirmed the issue was discovered internally and patched immediately with releases `pretix-newsletter` 2.0.1 and 1.6.3.
Bash and Code
1. Checking Installed Plugin Version
Activate your pretix virtual environment source /path/to/pretix/venv/bin/activate List installed plugins and grep for the newsletter plugin pip list | grep pretix-newsletter Expected vulnerable output: pretix-newsletter 1.5.0 Expected patched output: pretix-newsletter 2.0.1
2. Verifying the Patch via Docker (if applicable)
Check the version label on a running pretix Docker container
docker ps --filter "name=pretix" --format "table {{.Names}}\t{{.Image}}"
docker exec -it <pretix_container_name> pip show pretix-newsletter | grep Version
3. Simulating the Exploit (Conceptual – for educational purposes)
This represents the vulnerable template evaluation logic.
An attacker with template edit access would save a template containing:
malicious_payload = "{{ event.<strong>init</strong>.<strong>globals</strong>['config'].DATABASE_PASSWORD }}"
The vulnerable code would inappropriately evaluate this,
returning the actual password value instead of the string.
In a secure system, this should be blocked by a denylist or sandbox.
4. Rotating Secrets (Post-Patch)
After updating, change all secrets in pretix.cfg Edit the configuration file nano /path/to/pretix/pretix.cfg Example of lines to change: database.PASSWORD = NewStrongPasswordHere redis.PASSWORD = NewRedisPasswordHere secrets.SECRET_KEY = NewRandomSecretKey Restart the pretix service to apply changes systemctl restart pretix.service Or if using docker-compose: docker-compose down && docker-compose up -d
How Exploit
- Authenticate: Log in as a user with permissions to edit email templates (e.g., an event organizer).
- Craft Payload: Insert a Python object traversal payload into the email template subject or body, such as `{{event._config.password}}` or
{{event.__init__.__globals__}}. - Trigger Email: Initiate an action that sends the email (e.g., confirming an order or sending a newsletter).
- Exfiltrate Data: The email sent will contain the resolved value (e.g., the database password) in place of the payload, which the attacker can then read.
Protection from this CVE
Immediate Patching: Update the `pretix-newsletter` plugin to version 2.0.1 (or 1.6.3 for the legacy branch). This is the primary and only complete fix.
Rotate Credentials: As a precaution, immediately rotate all database passwords, API keys, and secret keys found in the `pretix.cfg` file, as they may have been compromised.
Restrict Backend Access: Limit the number of users with access to email template editing features to trusted personnel only.
Input Validation: As a defense-in-depth measure, ensure any user input used in templates is strictly validated, though this specific vulnerability requires a code-level fix.
Impact
A successful exploit allows an authenticated attacker with low privileges (template editor) to read the contents of the server’s `pretix.cfg` file. This file contains the application’s database credentials, Redis passwords, and Django SECRET_KEY. With these credentials, an attacker could gain direct, unauthorized access to the database, leading to a full data breach of all customer PII, order information, and payment details. Furthermore, possession of the `SECRET_KEY` could enable persistent cross-site scripting or other attacks against the application.
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Sources:
Reported By: nvd.nist.gov
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