The independent audit of Bitcoin Core delivered an unusually reassuring verdict: the reviewers found no critical or severe vulnerabilities in the software that keeps the Bitcoin network running, something extremely rare for such a large and complex codebase. The review, carried out by Quarkslab from May to September 2025 and funded by Brink with support from OSTIF, focused on the P2P layer and produced new testing tools that were warmly received within the community.

Independent Audit Finds No Critical Issues in Bitcoin Core

The process occupied roughly 100 man-days, with the team zooming in on the peer-to-peer layer—the part of the system that attackers are most likely to probe. Working together, Quarkslab researchers and contributors from Brink and Chaincode Labs formed a multidisciplinary group that set out to stress-test the software in a way that mirrors real-world pressures and adversarial scenarios.

Given Bitcoin Core’s long development history—more than 46,000 commits over 15 years—the auditors had both a large surface area to explore and a mature system to evaluate. Their approach mixed manual code reading, dynamic testing and aggressive fuzzing to uncover rare conditions, subtle inconsistencies and behaviors that only emerge under extreme inputs.

For the audit, new fuzz harnesses were specifically built to simulate difficult situations, such as chain reorganizations and complex block connections. Techniques like ensemble fuzzing and differential testing helped the team compare how the software behaves across multiple environments to catch unexpected differences in logic or performance.

The outcome was unusually positive. Only two low-level issues and a handful of recommendations surfaced, mostly aimed at clarity and thread-safety. According to the audit team, nothing in the findings suggested structural weaknesses or design flaws—only opportunities to refine an already solid foundation.

Alongside the report, the auditors delivered working improvements: new fuzzing tools, file-system tweaks and enhancements to the test suite. Many of these updates are already being incorporated into the Bitcoin Core codebase, strengthening the project’s ability to detect problems early and keep node operators safe at scale.

The community reaction mirrored the tone of the report—measured, optimistic and appreciative. Auditors openly praised the architecture and maturity of Bitcoin Core, while contributors highlighted the importance of long-term funding for security initiatives. This audit raises the standard for external reviews in the Bitcoin ecosystem, and the next step will be integrating the new testing tools into the main branch to validate their impact on performance and stability.