CVE-2020-5268

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

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.

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.

CVE-2020-5268 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.0.2, 2.7.0); upgrading removes the vulnerable code path.

Kodem intelligence

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Version 1.0.2 and 2.7.0 are patched.

1. What is CVE-2020-5268? CVE-2020-5268 is a medium-severity security vulnerability in Sustainsys.Saml2 (nuget), affecting versions < 1.0.2. It is fixed in 1.0.2, 2.7.0.
2. How severe is CVE-2020-5268? CVE-2020-5268 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of Sustainsys.Saml2 are affected by CVE-2020-5268? Sustainsys.Saml2 (nuget) versions < 1.0.2 is affected.
4. Is there a fix for CVE-2020-5268? Yes. CVE-2020-5268 is fixed in 1.0.2, 2.7.0. Upgrade to this version or later.
5. Is CVE-2020-5268 exploitable, and should I be worried? Whether CVE-2020-5268 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2020-5268 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2020-5268?
   • Upgrade Sustainsys.Saml2 to 1.0.2 or later
   • Upgrade Sustainsys.Saml2 to 2.7.0 or later

Other vulnerabilities in Sustainsys.Saml2