Security Digest · Vulnerability record
CVE-2026-54782: CoreWCF: Authentication bypass in CoreWCF SAML 1.1 / 2.0 token signature validation
CoreWCF is a port of the service side of Windows Communication Foundation (WCF) to .NET Core.
CVSS 10.0 Critical EPSS 0.4% · p35
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.4%, percentile 35: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 35% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes
CoreWCF.Primitives(NuGet) < 1.8.1, fixed in 1.8.1;CoreWCF.Primitives(NuGet) >= 1.9.0, < 1.9.1, fixed in 1.9.1. Check your lockfile, including transitive dependencies.
What it is
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 1.1 and SAML 2.0 token validation does not correctly resolve the issuer signing key or require signed tokens when IdentityConfiguration is used with federated bindings, allowing an unauthenticated remote attacker to impersonate any principal the trusted STS could issue. This issue is fixed in versions 1.8.1 and 1.9.1.
From the GitHub advisory
Impact Full impersonation of any principal the trusted STS could have issued an assertion for — including administrative principals when the relying party grants them via SAML claims. Affects both SAML 1.1 and SAML 2.0.
Preconditions Relying-party service is hosted with WSFederationHttpBinding or WS2007FederationHttpBinding (or any binding that triggers FederatedSecurityTokenManager for issued-token validation), and IdentityConfiguration is wired (UseIdentityConfiguration = true). Attacker can reach the service over the network and knows the trusted STS’s public certificate (public certs are by design discoverable).
Patches Fixed in CoreWCF v1.8.1 and v1.9.1
Workarounds None
Weakness type: CWE-290, CWE-347.
Product: CoreWCF.Primitives (NuGet) · Assigned by: GitHub_M · Published: 2026-07-08
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| NuGet | CoreWCF.Primitives | < 1.8.1 | 1.8.1 |
| NuGet | CoreWCF.Primitives | >= 1.9.0, < 1.9.1 | 1.9.1 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| CoreWCF | CoreWCF | >= 1.9.0, < 1.9.1, < 1.8.1 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 10 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N |
| GitHub | 3.1 | 10.0 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: changed (can affect other components)
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.41% probability of exploitation activity in the next 30 days; percentile 35.
Timeline
- — GitHub-reviewed advisory GHSA-xjr9-gg9q-jx3v published (critical)
- — CVE record published by GitHub_M
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-xjr9-gg9q-jx3v github.com
- CVE.org record CVE-2026-54782 cve.org
- NVD entry CVE-2026-54782 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com