CVE-2020-5268
Subject Confirmation Method not validated in Saml2 Authentication Services for ASP.NET
In Saml2 Authentication Services for ASP.NET versions before 1.0.2, and between 2.0.0 and 2.6.0, there is a vulnerability in how tokens are validated in some cases. 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 token to create a log in session. This vulnerability is patched in versions 1.0.2 and 2.7.0.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- Low
- User interaction
- Required
What an attacker can affect
- Confidentiality
- High
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
Subject Confirmation Method not validated in Saml2 Authentication Services for ASP.NET
In Saml2 Authentication Services for ASP.NET versions before 1.0.2, and between 2.0.0 and 2.6.0, there is a vulnerability in how tokens are validated in some cases. 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 token to create a log in session. This vulnerability is patched in versions 1.0.2 and 2.7.0.
- Record
CVE-2020-5268- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N - Weakness
- CWE-303
- Updated
- 2026-11-02
EUVDEUVD-2020-0374
In Saml2 Authentication Services for ASP.NET versions before 1.0.2, and between 2.0.0 and 2.6.0, there is a vulnerability in how tokens are validated in some cases. 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 token to create a log in session. This vulnerability is patched in versions 1.0.2 and 2.7.0.
- Record
EUVD-2020-0374- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N - Updated
- 2026-11-03
GitHub AdvisoriesGHSA-9475-xg6m-j7pw
Subject Confirmation Method not validated in Saml2 Authentication Services for ASP.NET
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 [email protected] if you think that there are further security issues.
- Record
GHSA-9475-xg6m-j7pw- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N - Weakness
- CWE-303
- Updated
- 2026-11-02
NVD
In Saml2 Authentication Services for ASP.NET versions before 1.0.2, and between 2.0.0 and 2.6.0, there is a vulnerability in how tokens are validated in some cases. 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 token to create a log in session. This vulnerability is patched in versions 1.0.2 and 2.7.0.
- Record
CVE-2020-5268- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N - CVSS 3.1
- 7.3 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N - CVSS 2.0
- 4.9 Medium
AV:N/AC:M/Au:S/C:P/I:P/A:N - Weakness
- CWE-303, CWE-287
- Updated
- 2026-11-02
OSV
In Saml2 Authentication Services for ASP.NET versions before 1.0.2, and between 2.0.0 and 2.6.0, there is a vulnerability in how tokens are validated in some cases. 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 token to create a log in session. This vulnerability is patched in versions 1.0.2 and 2.7.0.
- Record
CVE-2020-5268- CVSS 3.1
- 7.3 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N - Updated
- 2026-11-02
OSVGHSA-9475-xg6m-j7pw
Subject Confirmation Method not validated in Saml2 Authentication Services for ASP.NET
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 [email protected] if you think that there are further security issues.
- Record
GHSA-9475-xg6m-j7pw- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N - Weakness
- CWE-303
- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
Sustainsys.Saml2NuGet |
before 1.0.2 | 1.0.2 |
Sustainsys.Saml2NuGet |
2.0.0 up to 2.7.0 | 2.7.0 |
Sustainsys.Saml2NuGet |
before 1.0.2, plus listed versions 0.23.00.24.01.0.01.0.1 |
1.0.2 |
Sustainsys.Saml2NuGet |
2.0.0 up to 2.7.0, plus listed versions 2.1.02.2.02.3.02.4.02.5.02.6.0 |
2.7.0 |
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases, products | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2020-5268 is a medium vulnerability (CVSS 6.5) in Simplesamlphp Saml2, published April 21, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.09%, the 65th percentile. Fixed in Sustainsys.Saml2 1.0.2.