CVE-2020-5261 is a medium-severity (CVSS 6.8) CWE-294 vulnerability in Sustainsys.Saml2. O3 Security confirms whether CVE-2020-5261 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Missing Token Replay Detection in Saml2 Authentication services for ASP.NET
Real-World Exposure
Sustainsys.Saml2Real-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
Saml2 Authentication services for ASP.NET (NuGet package Sustainsys.Saml2) greater than 2.0.0, and less than version 2.5.0 has a faulty implementation of Token Replay Detection. Token Replay Detection is an important defence in depth measure for Single Sign On solutions. The 2.5.0 version is patched. Note that version 1.0.1 is not affected. It has a correct Token Replay Implementation and is safe to use. Saml2 Authentication services for ASP.NET (NuGet package Sustainsys.Saml2) greater than 2.0.0, and less than version 2.5.0 have a faulty implementation of Token Replay Detection. Token Replay Detection is an important defense measure for Single Sign On solutions. The 2.5.0 version is patched. Note that version 1.0.1 and prior versions are not affected. These versions have a correct Token Replay Implementation and are safe to use.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Sustainsys.Saml2 | ≥ 2.0.0&&< 2.5.0 | 2.5.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Sustainsys.Saml2. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update Sustainsys.Saml2 to 2.5.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-5261 is resolved across your whole dependency graph.
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.
How O3 protects you
O3 pinpoints whether CVE-2020-5261 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2020-5261. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2020-5261 in your dependencies?
O3 detects CVE-2020-5261 across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.