Best Security Audit Companies

Important

On June 1, 2026, we published our third-party security audit conducted by Cure53, widely regarded as one of the best security research firms in the industry. The full pentest report is available at pentest-report_forward-email.pdf. Forward Email is the only 100% open-source email service with an independently verified security audit.

Overview

Forward Email has been evaluating cybersecurity research companies to audit our open-source codebase on GitHub and server infrastructure. After several years of research, we identified several security audit firms with consistent high-quality work, technical expertise, and values that match our privacy focus.

This document shares our findings and recommendations for organizations seeking professional security audit services. Each company listed here does strong work in penetration testing, code review, infrastructure assessment, and security research.

Our Evaluation Process

We examined each company's track record, technical expertise, transparency in reporting, and commitment to open-source principles. The companies featured in this guide performed consistently well during our multi-year evaluation period.

The companies listed below are not ranked in any particular order. Each has its own strengths and specializations, and the best choice depends on specific project requirements, budget considerations, and organizational needs.

Cure53

Location: Berlin, Germany Website: https://cure53.de/ Specialization: "Fine penetration tests for fine websites"

Cure53 is a German cybersecurity firm known for meticulous web application security testing and penetration testing. Based in Berlin, they are known for thorough testing methodologies and detailed reports.

The company has performed security assessments for high-profile clients and open-source projects, covering modern web technologies, cryptographic implementations, and infrastructure security. Cure53's reports stand out for their technical depth and actionable recommendations.

Notable Publications and Reports:

Radically Open Security

Location: Amsterdam, The Netherlands Website: https://www.radicallyopensecurity.com/ Specialization: "Non-Profit Computer Security Consultancy"

Radically Open Security (ROS) is a non-profit computer security consultancy that follows open-source principles and transparency values. Based in Amsterdam, ROS publishes its methodologies and findings whenever possible.

Their non-profit model lets them focus on security outcomes instead of profit, which often results in more thorough assessments and candid recommendations. ROS has particular expertise in privacy-focused technologies, VPN services, and applications that handle sensitive user data.

Notable Publications and Reports:

Assured AB

Location: Gothenburg, Sweden Website: https://www.assured.se/ Specialization: "Experts in technical cybersecurity"

Assured AB is a Swedish cybersecurity consultancy specializing in technical cybersecurity assessments. Based in Gothenburg, they focus on email infrastructure, DNS security, and API assessments.

The company pairs thorough technical analysis with practical recommendations. Their reports show close attention to detail and a strong grasp of modern security threats and mitigation strategies.

Notable Publications and Reports:

Trail of Bits

Location: New York, New York, United States Website: https://www.trailofbits.com/ Specialization: "We don't just fix bugs, we fix software."

Trail of Bits is an American cybersecurity firm focused on software security. Based in New York, they have built widely used security tools and methodologies. Their motto, "We don't just fix bugs, we fix software," reflects their focus on systemic security issues over surface-level vulnerabilities.

The company has particular expertise in blockchain security, cryptographic implementations, and complex software systems. Trail of Bits also contributes open-source security tools and publishes research on emerging security domains.

Notable Publications and Reports:

Company Comparison

Company Location Focus Area Notable Strengths Public Reports
Cure53 Berlin, Germany Web Application Security Detailed penetration testing, comprehensive reporting 3+ Mullvad assessments
Radically Open Security Amsterdam, Netherlands Privacy & Open Source Non-profit model, transparency, VPN expertise Public methodology sharing
Assured AB Gothenburg, Sweden Technical Infrastructure Email/DNS security, API assessments Specialized server audits
Trail of Bits New York, USA Software Security Blockchain, cryptography, security tooling Open-source contributions

Selection Criteria

We weighed these factors, which any organization selecting a security partner should also assess:

Technical Expertise: All recommended companies have technical knowledge across multiple domains including web application security, infrastructure assessment, cryptographic implementations, and emerging technologies.

Transparency and Reporting: Each firm provides thorough, actionable reports that communicate findings, risk assessments, and remediation strategies. Many also contribute to the broader security community through public research and open-source tools.

Track Record: The companies listed have worked with high-profile clients on complex security problems. Their public reports demonstrate consistent quality and thoroughness.

Alignment with Values: For organizations prioritizing privacy, open-source principles, and transparency, these companies have shown commitment to these values through their work and business practices.

Continuous Improvement: All recommended firms stay current with new threats and emerging technologies, so their assessments stay relevant.

We recommend organizations conduct their own evaluation based on specific needs, budget constraints, and project requirements. Any of these companies can provide strong security assessments for organizations protecting their infrastructure and user data.