How severe is CVE-2020-5268?

CVE-2020-5268 has a CVSS score of 7.3/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2020-5268?

CVE-2020-5268 affects the following packages: Sustainsys.Saml2 (NuGet), Sustainsys.Saml2 (NuGet). Ecosystems affected: NuGet.

How do I fix CVE-2020-5268?

Update Sustainsys.Saml2 to 1.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-5268 is resolved across your whole dependency graph.

How do I detect CVE-2020-5268 in my NuGet dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Sustainsys.Saml2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2020-5268 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2020-5268 actively exploited in the wild?

No public exploit code has been indexed for CVE-2020-5268 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2020-5268?

CVE-2020-5268 has an EPSS (Exploit Prediction Scoring System) score of 1.1%, placing it in the 65th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2020-5268?

CVE-2020-5268 is classified as CWE-303 (CWE-303), Improper Authentication (CWE-287). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2020-5268 published, and has it been updated?

CVE-2020-5268 was published on April 21, 2020 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

.NET

.NET NuGet

Not in CISA KEV

HIGH severity

CVE-2020-5268 — Sustainsys.Saml2

HIGHFix: Sustainsys/Saml2@e58e0a1

CVE-2020-5268 is a high-severity (CVSS 7.3) CWE-303 vulnerability in Sustainsys.Saml2. A fix is available for Sustainsys.Saml2 — see the affected versions and patch details below.

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

Also known asGHSA-9475-xg6m-j7pw

Published

Apr 21, 2020

Updated

Oct 20, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 31, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.1%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs65th percentile — riskier than 65% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

.NETSustainsys.Saml2.NETSustainsys.Saml2

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.

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:

Comment on #103
Email us at [email protected] if you think that there are further security issues.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
.NETNuGet	`Sustainsys.Saml2`	all versions	1.0.2`dotnet add package Sustainsys.Saml2 --version 1.0.2`
.NETNuGet	`Sustainsys.Saml2`	≥ 2.0.0&&< 2.7.0	2.7.0`dotnet add package Sustainsys.Saml2 --version 2.7.0`

Affected Products

1 product · 2 configurations

Application

saml2sustainsys

≥ 2.0.0 && < 2.7.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Sustainsys.Saml2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Sustainsys.Saml2 to 1.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-5268 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### 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 at