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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2020-5268: 1.09% estimated exploitation activity in the next 30 days; percentile 65.34 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

22 Apr 2020, 20:59 UTC

Last modified by the source

9 Jan 2023, 05:02 UTC

Source last checked

26 Oct 2026, 16:58 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9475-xg6m-j7pw

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# Patch Next advisory brief: CVE-2020-5268

Advisory: Subject Confirmation Method not validated in Saml2 Authentication Services for ASP.NET
IDs: CVE-2020-5268, GHSA-9475-xg6m-j7pw
Record: https://patchnext.com/advisories/cve-2020-5268 (revision 1, source checked 26 Oct 2026, 16:58 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: sustainsys.saml2 2.7.0, 1.0.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet sustainsys.saml2: affected < 1.0.2; >= 2.0.0, < 2.7.0; fixed in 1.0.2, 2.7.0

## Suggested inspection (read-only)
- NuGet sustainsys.saml2: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on sustainsys.saml2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9475-xg6m-j7pw (GitHub-reviewed advisory GHSA-9475-xg6m-j7pw lists affected ranges: NuGet sustainsys.saml2 >=0 =2.0.0 <2.7.0)

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