ServiceStack before 5.9.2 mishandles JWT signature verification unless an application has a custom ValidateToken function that establishes a valid minimum length for a signature.

References

• https://nvd.nist.gov/vuln/detail/CVE-2020-28042
• ServiceStack/ServiceStack@540d406
• https://forums.servicestack.net/t/servicestack-v5-9-2-released/8850
• https://snyk.io/vuln/SNYK-DOTNET-SERVICESTACK-1035519
• https://www.nuget.org/packages/ServiceStack/
• https://www.shielder.it/advisories/servicestack-jwt-signature-verification-bypass/
• https://www.shielder.it/blog/2020/11/re-discovering-a-jwt-authentication-bypass-in-servicestack/