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CVE-2020-5268 — Vulnerability in Sustainsys.Saml2 — CVE Details

MEDIUM

Subject Confirmation Method not validated in Saml2 Authentication Services for ASP.NET

Published April 22, 2020Updated September 10, 2026Source: osv

Summary

### Impact Saml2 tokens are usually used as bearer tokens - a caller that presents a token is assumed to be the subject of the token. There is also support in the Saml2 protocol for issuing tokens that is tied to a subject through other means, e.g. holder-of-key where possession of a private key must be proved. The Sustainsys.Saml2 library incorrectly treats all incoming tokens as bearer tokens, even though they have another subject confirmation method specified. This could be used by an attacker that could get access to Saml2 tokens with another subject confirmation method than bearer. The attacker could then use such a tocken to create a log in session. ### Patches Version 1.0.2 and 2.7.0 are patched. ### Workarounds Ensure that any IdentityProvider trusted by the Sustainsys.Saml2 SP only issues bearer tokens if the audience matches the Sustainsys.Saml2 SP. ### For more information If you have any questions or comments about this advisory: * Comment on #103 * Email us at security@sustainsys.com if you think that there are further security issues.

Advisory Timeline

  • First published April 22, 2020 (2364 days ago).
  • Last revised September 10, 2026 — 2331 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

NuGet
Update Sustainsys.Saml2 to 2.7.0 or later
dotnet add package Sustainsys.Saml2 --version 2.7.0
NuGet
Update Sustainsys.Saml2 to 1.0.2 or later
dotnet add package Sustainsys.Saml2 --version 1.0.2

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

Affected Packages (2)

Affects 1 ecosystem: nuget (1).

PackageEcosystemAffectedFixed In
Sustainsys.Saml2
nuget
2.0.0, 2.1.0, 2.2.0, 2.3.0 (+3 more)2.7.0
Sustainsys.Saml2
nuget
0.23.0, 0.24.0, 1.0.0, 1.0.11.0.2

Vulnerability Classification

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

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 6.5 score means for each attack dimension.

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

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

Frequently Asked Questions

What is CVE-2020-5268?
Subject Confirmation Method not validated in Saml2 Authentication Services for ASP.NET This vulnerability has been assigned a severity rating of MEDIUM (CVSS score: 6.5/10).
How do I check if my project is affected by CVE-2020-5268?
CVE-2020-5268 affects Sustainsys.Saml2. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2020-5268 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
6.5

Exploitation requires specific conditions or has limited impact. Remediate within weeks.

Also Known As

GHSA-9475-xg6m-j7pw

Related CVEs

  • CVE-2023-41890
    HIGH

    Sustainsys.Saml2 Insufficient Identity Provider Issuer Validation

  • CVE-2020-5261
    HIGH

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

  • CVE-2026-106111
    MEDIUM

    ImageSharp: EXR ZIP decoder can expose stale allocator data after a short inflate

  • CVE-2026-65829
    MEDIUM

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