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.NET
.NET NuGet
Not in CISA KEV
HIGH severity

CVE-2023-41890 — Sustainsys.Saml2

HIGH

CVE-2023-41890 is a high-severity (CVSS 7.5) CWE-289 vulnerability in Sustainsys.Saml2. A fix is available for Sustainsys.Saml2 — see the affected versions and patch details below.

Sustainsys.Saml2 Insufficient Identity Provider Issuer Validation

Also known asGHSA-fv2h-753j-9g39
Published
Updated
Affected
3 pkgs
Patched
2 / 3
Exploits
None indexed
Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2023-41890.

EPSS Exploitation Probability

via FIRST.org ↗
0.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs55th percentile — riskier than 55% of all scored CVEsHighest risk
0.00%0.42%0.83%1.25%0.1%0.8%May 26Sep 26Nov 26

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

3 pkgs affected
.NETSustainsys.Saml2.NETSustainsys.Saml2.NETKentor.AuthServices

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

Sustainsys.Saml2 library adds SAML2P support to ASP.NET web sites, allowing the web site to act as a SAML2 Service Provider. Prior to versions 1.0.3 and 2.9.2, when a response is processed, the issuer of the Identity Provider is not sufficiently validated. This could allow a malicious identity provider to craft a Saml2 response that is processed as if issued by another identity provider. It is also possible for a malicious end user to cause stored state intended for one identity provider to be used when processing the response from another provider. An application is impacted if they rely on any of these features in their authentication/authorization logic: the issuer of the generated identity and claims; or items in the stored request state (AuthenticationProperties). This issue is patched in versions 2.9.2 and 1.0.3. The AcsCommandResultCreated notification can be used to add the validation required if an upgrade to patched packages is not possible.

Affected Packages

3 total 2 fixed
EcosystemPackageVulnerable rangeFix
.NETNuGetSustainsys.Saml2all versions1.0.3dotnet add package Sustainsys.Saml2 --version 1.0.3
.NETNuGetSustainsys.Saml2≥ 2.0.0&&< 2.9.22.9.2dotnet add package Sustainsys.Saml2 --version 2.9.2
.NETNuGetKentor.AuthServicesall versionsNo fix

Affected Products

1 product · 2 configurations
Application
saml2sustainsys
≥ 2.0.0 && < 2.9.2
range

Detection & mitigation playbook

Open-source dependency

  1. 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.

  2. Fix

    Update Sustainsys.Saml2 to 1.0.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-41890 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

Sustainsys.Saml2 library adds SAML2P support to ASP.NET web sites, allowing the web site to act as a SAML2 Service Provider. Prior to versions 1.0.3 and 2.9.2, when a response is processed, the issuer of the Identity Provider is not sufficiently validated. This could allow a malicious identity provider to craft a Saml2 response that is processed as if issued by another identity provider. It is also possible for a malicious end user to cause stored state intended for one identity provider to be used when processing the response from another provider. An application is impacted if they rely on
O3 Security · Impact-Aware SCA

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CVE-2023-41890: Sustainsys.Saml2 — Fixed in 1.0.3