CVE-2020-28042 is a medium-severity (CVSS 5.3) CWE-347 vulnerability in ServiceStack. 3 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for ServiceStack — see the affected versions and patch details below.
Signature validation bypass in ServiceStack
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
ServiceStackReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | ServiceStack | all versions | 5.9.2dotnet add package ServiceStack --version 5.9.2 |
Affected Products
servicestackservicestackResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ServiceStack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ServiceStack to 5.9.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-28042 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2020-28042 in your dependencies?
Find it across NuGet, including transitive dependencies.