CVE-2026-54779 is a medium-severity (CVSS 5.9) CWE-294 vulnerability in CoreWCF.Primitives. A fix is available for CoreWCF.Primitives — see the affected versions and patch details below.
CoreWCF: SAML token replay protection is inoperative
Exploitation Status
No confirmed exploitation observed yet
- 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-2026-54779.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-54779 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,308 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
CoreWCF.Primitives.NETCoreWCF.PrimitivesReal-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
CoreWCF is a port of the service side of Windows Communication Foundation (WCF) to .NET Core. Prior to 1.8.1 and 1.9.1, CoreWCF SAML token replay protection is inoperative because DefaultTokenReplayCache.TryAdd does not reject duplicate tokens when DetectReplayedTokens is enabled, allowing a captured token to be reused. This issue is fixed in versions 1.8.1 and 1.9.1.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | CoreWCF.Primitives | all versions | 1.8.1dotnet add package CoreWCF.Primitives --version 1.8.1 |
| .NETNuGet | CoreWCF.Primitives | ≥ 1.9.0&&< 1.9.1 | 1.9.1dotnet add package CoreWCF.Primitives --version 1.9.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for CoreWCF.Primitives, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update CoreWCF.Primitives to 1.8.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-54779 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
Is CVE-2026-54779 in your dependencies?
Find it across NuGet, including transitive dependencies.