Detect CoreWCF SAML Token Signature Validation Authentication Bypass (CVE-2026-54782) in Sumo Logic CSE
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
Sumo Detection Query
_sourceCategory=*windows* OR _sourceCategory=*iis* OR _sourceCategory=*dotnet*
| where _raw matches /(?i)(CoreWCF|System\.ServiceModel|SAML|WSTrust|assertion)/
| parse regex field=_raw "(?i)(?<event_type>signature.*?invalid|unsigned.*?assertion|bypass.*?auth|SecurityTokenValidationException|anonymous.*?access)" nodrop
| where !isEmpty(event_type)
| parse regex field=_raw "(?i)(?:src[= ]+|source[= ]+|client[= ]+)(?<src_ip>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})" nodrop
| parse regex field=_raw "(?i)(?:user[= ]+|username[= ]+)(?<username>[\w@\.\-]+)" nodrop
| timeslice 5m
| count by _timeslice, src_ip, username, event_type
| sort by _count descSumo Logic query searching Windows, IIS, and .NET application logs for CoreWCF SAML signature bypass indicators, parsed into structured fields for correlation and alerting.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate SAML SLO (Single Logout) flows generating token parsing warnings
- Clock skew between IdP and SP causing SAML assertion timestamp validation failures
- Vendor security assessments targeting WCF service 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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