What’s Vulnerable › Vulnerabilities

CVE-2020-28042

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2020-11-02 · updated 2026-06-17
• Weakness: CWE-347

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 products

• ServiceStack: before 5.9.2 — fixed in 5.9.2

How to fix

Upgrade to a fixed version: ServiceStack 5.9.2. Check the vendor advisory for mitigations.

References

• https://forums.servicestack.net/t/servicestack-v5-9-2-released/8850
• https://github.com/ServiceStack/ServiceStack/commit/540d4060e877a03ae95343c1a8560a26768585ee
• 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/
• https://forums.servicestack.net/t/servicestack-v5-9-2-released/8850
• https://github.com/ServiceStack/ServiceStack/commit/540d4060e877a03ae95343c1a8560a26768585ee
• 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/

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