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CVE-2020-5261 — Missing Token Replay Detection in Sustainsys.Saml2...

HIGH

Missing Token Replay Detection in Saml2 Authentication services for ASP.NET

Published March 25, 2020Updated July 8, 2026Source: osv

Summary

### Impact Token Replay Detection is an important defence in depth measure for Single Sign On solutions. In all previous 2.X versions, the Token Replay Detection is not properly implemented. Note that version 1.0.1 is not affected. It has a correct Token Replay Implementation and is safe to use. ### Patches The 2.5.0 version is patched. ### Workarounds There are no workarounds with existing versions. Fixing the issue requires code updates. ### References https://en.wikipedia.org/wiki/Replay_attack ### For more information If you have any questions or comments about this advisory: * Comment on #711. * Email us at [security@sustainsys.com](mailto:security@susatinsys.com) if you think that there are further security issues.

Advisory Timeline

  • First published March 25, 2020 (2392 days ago).
  • Last revised July 8, 2026 — 2296 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

NuGet
Update Sustainsys.Saml2 to 2.5.0 or later
dotnet add package Sustainsys.Saml2 --version 2.5.0

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (1)

Affects 1 ecosystem: nuget (1).

PackageEcosystemAffectedFixed In
Sustainsys.Saml2
nuget
2.0.0, 2.1.0, 2.2.0, 2.3.0 (+1 more)2.5.0

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 8.2 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N

References

Frequently Asked Questions

What is CVE-2020-5261?
Missing Token Replay Detection in Saml2 Authentication services for ASP.NET This vulnerability has been assigned a severity rating of HIGH (CVSS score: 8.2/10).
How do I check if my project is affected by CVE-2020-5261?
CVE-2020-5261 affects Sustainsys.Saml2. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2020-5261 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
8.2

High exploitability or significant impact. Prioritize remediation within days.

Also Known As

GHSA-g6j2-ch25-5mmv

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