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

Moderate severity GitHub Reviewed Published Apr 21, 2020 in Sustainsys/Saml2 • Updated Jan 9, 2023

Package

nuget Sustainsys.Saml2 (NuGet)

Affected versions

< 1.0.2
>= 2.0.0, < 2.7.0

Patched versions

1.0.2
2.7.0

Description

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:

References

@AndersAbel AndersAbel published to Sustainsys/Saml2 Apr 21, 2020
Reviewed Apr 21, 2020
Published to the GitHub Advisory Database Apr 22, 2020
Last updated Jan 9, 2023

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
Low
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N

EPSS score

0.131%
(49th percentile)

Weaknesses

CVE ID

CVE-2020-5268

GHSA ID

GHSA-9475-xg6m-j7pw

Source code

No known source code
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