GHSA-6r78-m64m-qwcf: 
C# vulnerability analysis and mitigation

Moq versions 4.20.0-rc through 4.20.1 included a feature called SponsorLink that collected user data without consent. The vulnerability was discovered in August 2023 when it was found that the library was running an obfuscated DLL at build time that scanned local git config data and shared users' hashed email addresses with SponsorLink's remote servers, with no option to disable this functionality (GitHub Advisory).

The vulnerability involved SponsorLink functionality that would execute during build time to collect git configuration data. Specifically, it would run 'git config --get user.email' to obtain the user's email address, hash it using SHA256, and transmit this data to Azure Blob storage. The implementation included checks for network availability and git configuration, but provided no opt-out mechanism (SponsorLink Blog).

The vulnerability raised significant privacy and security concerns, particularly regarding GDPR compliance, as it collected and transmitted personal information without user consent. The issue affected build processes and potentially exposed user email data, even in hashed form, to third-party servers. Additionally, it caused build performance impacts and could break builds in environments with restricted network access (GitHub Issues).

While this was not a traditional security exploit, the functionality was automatically executed during build time for affected versions, making it immediately active for all users of the affected versions. The data collection occurred without user awareness or consent, affecting any development environment using the compromised versions (GitHub Advisory).

The issue was resolved in Moq version 4.20.2, which completely removed the SponsorLink functionality. Users should upgrade to version 4.20.2 or later to ensure the data collection is no longer present. For those unable to upgrade immediately, the only workaround was to continue using versions prior to 4.20.0-rc (GitHub PR).

The community reaction was overwhelmingly negative, with many developers expressing concerns about privacy violations and trust breach. The incident led to numerous organizations considering or implementing replacements for Moq in their projects. The controversy sparked broader discussions about open-source sustainability and appropriate methods for supporting open-source projects (GitHub Issues).