What’s Vulnerable › Vulnerabilities

CVE-2020-5261: Missing Token Replay Detection

• Severity: medium (CVSS 6.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-03-25 · updated 2026-06-17
• Weakness: CWE-294

Description

Saml2 Authentication services for ASP.NET (NuGet package Sustainsys.Saml2) greater than 2.0.0, and less than version 2.5.0 has a faulty implementation of Token Replay Detection. Token Replay Detection is an important defence in depth measure for Single Sign On solutions. The 2.5.0 version is patched. Note that version 1.0.1 is not affected. It has a correct Token Replay Implementation and is safe to use. Saml2 Authentication services for ASP.NET (NuGet package Sustainsys.Saml2) greater than 2.0.0, and less than version 2.5.0 have a faulty implementation of Token Replay Detection. Token Replay Detection is an important defense measure for Single Sign On solutions. The 2.5.0 version is patched. Note that version 1.0.1 and prior versions are not affected. These versions have a correct Token Replay Implementation and are safe to use.

Affected products

• Sustainsys Saml2: from 2.0.0 before 2.5.0 — fixed in 2.5.0

How to fix

Upgrade to a fixed version: Sustainsys Saml2 2.5.0. Check the vendor advisory for mitigations.

References

• https://github.com/Sustainsys/Saml2/commit/e58e0a1aff2b1ead6aca080b7cdced55ee6d5241
• https://github.com/Sustainsys/Saml2/issues/711
• https://github.com/Sustainsys/Saml2/security/advisories/GHSA-g6j2-ch25-5mmv
• https://github.com/Sustainsys/Saml2/commit/e58e0a1aff2b1ead6aca080b7cdced55ee6d5241
• https://github.com/Sustainsys/Saml2/issues/711
• https://github.com/Sustainsys/Saml2/security/advisories/GHSA-g6j2-ch25-5mmv

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