Detect CoreWCF SAML Token Signature Validation Authentication Bypass (CVE-2026-54782) in Elastic Security
CVE-2026-54782 is a critical (CVSS 10.0) authentication bypass vulnerability in CoreWCF.Primitives affecting SAML 1.1 and 2.0 token signature validation. An unauthenticated attacker can craft a SAML assertion with an invalid or missing signature that CoreWCF accepts as valid, bypassing all authentication controls on WCF service endpoints. Affects CoreWCF.Primitives < 1.8.1 and >= 1.9.0, < 1.9.1. A public PoC exists.
MITRE ATT&CK
Elastic Detection Query
sequence by host.name, user.name with maxspan=5m
[network where network.protocol in ("http", "https") and
destination.port in (80, 443, 808, 8080, 9000) and
url.path like~ "*saml*" or url.path like~ "*wstrust*" or url.path like~ "*sts*"]
[process where process.name in ("w3wp.exe", "dotnet.exe") and
process.args like~ "*CoreWCF*" or process.args like~ "*System.ServiceModel*"]
[any where event.dataset == "windows.application" and
message like~ "*SAML*" and
(message like~ "*bypass*" or message like~ "*invalid signature*" or message like~ "*unsigned*")]EQL sequence detection correlating inbound SAML-path HTTP requests to a CoreWCF .NET worker process followed by an application log event indicating signature validation failure or bypass, all within a 5-minute window.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate federated authentication flows generating transient SAML validation warnings
- Certificate rotation events causing temporary signature verification failures
- Automated integration tests replaying SAML assertions against WCF test endpoints
Other platforms for CVE-2026-54782
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Send Unsigned SAML 2.0 Assertion to CoreWCF Endpoint
Expected signal: IIS logs show POST /Service with HTTP 200 response; Windows Application Event Log shows no SecurityTokenValidationException; network capture shows SAML assertion without Signature element accepted
- Test 2Send Stripped Signature SAML 1.1 Token to CoreWCF wsHttpBinding Endpoint
Expected signal: Network capture shows WS-Security SOAP header with SAML 1.1 assertion lacking Signature; IIS or Kestrel logs show HTTP 200; no authentication failure event in Windows Security log
- Test 3Deploy Vulnerable CoreWCF Version and Validate Authentication Bypass via PoC
Expected signal: dotnet process spawned on port 5050; curl returns echo response without authentication challenge on 1.8.0; after patching to 1.8.1 the same request returns 401 or SOAP fault
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