Authentication Bypass in CoreWCF.Primitives (CVE-2026-54781)
Summary
Authentication bypass in CoreWCF.Primitives (CVE-2026-54781). Confidential information can be exposed externally. Mitigation: upgrade to 1.9.1 or later.
Original description
The description as published by the source.
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 validation does not enforce SubjectConfirmation method URIs or holder-of-key proof keys in SamlSecurityTokenHandler, allowing holder-of-key downgrade or custom confirmation method assertions to authenticate a subject without proving authority over the assertion. This issue is fixed in versions 1.8.1 and 1.9.1.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-54781 has been found in CoreWCF.Primitives.
Confidential information can be exposed externally. CVSS score: 7.4/10.
What to do: upgrade CoreWCF.Primitives to 1.9.1 or later.
If unsure, ask your IT team or search "CoreWCF.Primitives CVE-2026-54781" on the vendor's site.
CVE-2026-54781 (CoreWCF.Primitives) — CWE-287 / CVSS v3 7.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 1.9.1 — apply immediately
Workaround: To exploit this issue, it's required that a trusted STS issues SAML assertions whose SubjectConfirmationMethod is not one of the SAML 1.1 trio, or is willing to issue holder-of-key assertions without KeyInfo.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Authentication bypass (CWE-287) exists in CoreWCF.Primitives.
Check the vendor advisory for the affected versions of CoreWCF.Primitives.
Severity: High (CVSS 7.4/10). Confidential information can be exposed externally.
Update to 1.9.1.
Workaround: To exploit this issue, it's required that a trusted STS issues SAML assertions whose SubjectConfirmationMethod is not one of the SAML 1.1 trio, or is willing to issue holder-of-key assertions without KeyInfo.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'CoreWCF.Primitives' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'CoreWCF.Primitives' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
CoreWCF.Primitivesを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply temporary workaround mitigate
To exploit this issue, it's required that a trusted STS issues SAML assertions whose SubjectConfirmationMethod is not one of the SAML 1.1 trio, or is willing to issue holder-of-key assertions without KeyInfo.パッチが適用されるまでの応急処置として、To exploit this issue, it's required that a trusted STS issues SAML assertions whose SubjectConfirmationMethod is not one of the SAML 1.1 trio, or is willing to issue holder-of-key assertions without KeyInfo. を実施。回避策の副作用 (機能低下) を確認した上で。
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3Apply patch patch
Upgrade CoreWCF.Primitives to 1.9.1ステージング環境で 1.9.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
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4Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov
- package github.com
- patch github.com
- patch github.com
- patch github.com
- web github.com
- web github.com
- web github.com