At Postbox, security isn’t a checklist; it’s a fundamental property of our architecture. We treat form data as a contract, and protecting that contract is our primary directive.
In April 2026, we completed our biannual internal security audit. This report outlines our findings, our resolutions, and the core philosophies that keep our infrastructure resilient against modern threats.
Audit Methodology
We performed a deep-stack audit of the Postbox platform, focusing on the boundary between public endpoints and internal data processing. Our methodology combined automated scanning with manual line-by-line review of our most sensitive code paths.
Scope of Review
- Identity & Access: OAuth 2.1 implementation, session lifecycle, and API key isolation.
- Data Integrity: Tenant isolation, submission encryption, and soft-delete safety.
- Infrastructure: TLS cert pinning, DNS validation, and container hardening.
- Application Security: XSS/SSRF prevention, SQL injection vectors, and rate-limiting robustness.
Executive Summary
| Severity | Findings | Status |
|---|---|---|
| Critical | 0 | N/A |
| High | 2 | Resolved |
| Medium | 5 | Resolved |
| Low | 5 | Resolved |
| Info | 9 | Logged |
Zero critical vulnerabilities were found. All High and Medium findings were patched and verified within 24 hours of discovery.
Scenario: The DNS Rebinding Threat
During the audit, we identified a potential edge case in our Webhook Delivery System. While we validated destination URLs at the time of creation, a sophisticated attacker could use a “DNS Rebinding” technique to change the IP address of their domain between the time of validation and the time of delivery, potentially tricking our system into hitting internal services.
The Resolution: DNS Pinning
We implemented a proactive DNS Pinning strategy. Now, when a webhook is triggered:
- The system resolves the hostname once.
- It validates the IP address against a strict blacklist of private and reserved ranges.
- It performs the delivery directly to that validated IP, ignoring any subsequent DNS changes.
This “Resolve-then-Deliver” pattern is part of our commitment to zero-trust architecture.
Technical Hardening Results
Session Resilience
We tightened our session management to prevent long-term replay attacks. All session cookies now enforce a server-side max_age, ensuring that even if a browser is compromised and cookies are extracted, the window of utility for an attacker is strictly limited.
Rate Limiting Accuracy
We discovered that our rate limiter was occasionally misidentifying client IPs due to complex proxy chains. We’ve updated our ingestion logic to correctly interpret X-Forwarded-For headers, ensuring that rate limits are applied fairly and accurately to the true source of traffic.
Infrastructure Isolation
The audit confirmed that our database layer remains completely isolated. We use verify_peer with certificate pinning for all internal connections, meaning that even if an attacker gained access to our application network, they would be unable to intercept or spoof database traffic.
Our Security Stack
To maintain this standard, we integrate security into our daily CI/CD pipeline using industry-leading tools:
- Sobelow: Specialized static analysis for Phoenix/Elixir security.
- Mix Audit: Continuous monitoring of our dependency tree for known vulnerabilities.
- Dialyzer: Strong type checking to prevent runtime data-shape errors.
- Manual Peer Review: Every change to an authentication or data path requires two-party sign-off.
Looking Ahead
While this audit was successful, the threat landscape is constantly evolving. In the coming months, we are moving toward:
- Third-Party Penetration Testing: Engaging external researchers to stress-test our assumptions.
- SOC 2 Type II Compliance: Formally codifying our security procedures for enterprise partners.
- Bug Bounty Program: Incentivizing the global research community to help us keep Postbox secure.
Trust is our most valuable asset. If you have questions about our security posture or want to report a vulnerability, please reach out to our security team directly. Contact Security or Start Building with Postbox.