# CVE-2026-54784: CoreWCF cleartext proof key exposure in SPNEGO negotiation

Source: https://junglewise.ai/threats/cve-2026-54784-corewcf-cleartext-proof-key-exposure-in-spnego-negotiation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-08. Updated: 2026-07-08  
License: CC BY 4.0 with a link back

CVE-2026-54784 · Severity: high · CVSS 7.4 · Published 2026-07-08

CoreWCF is a modern implementation of Windows Communication Foundation (WCF) for .NET Core, used to build networked services. A security flaw in version 1.9.0 fails to properly encrypt sensitive session keys during the authentication process when using Windows credentials. This allows a network attacker to intercept these keys, potentially enabling them to impersonate legitimate users and read or modify private communications.

Technologies: [CoreWCF](https://junglewise.ai/threats/technologies/corewcf), [CoreWCF.Primitives (NuGet)](https://junglewise.ai/threats/technologies/corewcf-primitives). Vendors: [CoreWCF](https://junglewise.ai/threats/vendors/corewcf), [NuGet](https://junglewise.ai/threats/vendors/nuget).

## Quick answers

**Is CVE-2026-54784 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-54784 being exploited in the wild.

**How severe is CVE-2026-54784?** High severity, with a CVSS score of 7.4, published 8 July 2026.

**Which products and versions are affected?** CoreWCF >= 1.9.0, < 1.9.1; CoreWCF.Primitives (NuGet) >= 1.9.0, < 1.9.1, ECOSYSTEM:introduced=1.9.0,fixed=1.9.1.

**Is there a fix for CVE-2026-54784?** Yes. CoreWCF.Primitives (NuGet): upgrade to 1.9.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-54784 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-54784?** Check whether you run CoreWCF or CoreWCF.Primitives (NuGet) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- CoreWCF.Primitives (NuGet): upgrade to 1.9.1 or later

  ```sh
  dotnet add package CoreWCF.Primitives --version 1.9.1
  ```


## Technical details

A vulnerability exists in CoreWCF 1.9.0 where SPNEGO SecurityContextToken (SCT) negotiation fails to encrypt the proof key recovered from the Request Security Token Response (RSTR). This occurs when using TransportWithMessageCredential with Windows client credentials and session establishment. The root cause is a failure in the .NET 8 facade to request encryption during the NegotiateAuthentication.Wrap call, resulting in an integrity-only (MIC) token that leaves the proof key in cleartext. A passive network observer on a non-TLS connection can recover the symmetric SCT session key to impersonate the authenticated Windows principal and decrypt or forge WS-SecureConversation traffic. The issue is fixed in version 1.9.1 by ensuring the requestEncryption parameter is set to true.

## Affected products

- CoreWCF CoreWCF >= 1.9.0, < 1.9.1

## Identifiers

- CVE-2026-54784
- GHSA-2288-8h3r-cqgg

## Timeline

- 2026-07-08: advisory: NVD publication date
- 2026-06-16: patched: Release of version 1.9.1

## References

- [https://github.com/CoreWCF/CoreWCF/commit/2afae08b2fa5288428df89e8161116b816cf6b4b](https://github.com/CoreWCF/CoreWCF/commit/2afae08b2fa5288428df89e8161116b816cf6b4b)
- [https://github.com/CoreWCF/CoreWCF/commit/f216aa6929d41dc99cee098b1e69c260ec4c41c7](https://github.com/CoreWCF/CoreWCF/commit/f216aa6929d41dc99cee098b1e69c260ec4c41c7)
- [https://github.com/CoreWCF/CoreWCF/releases/tag/v1.9.1](https://github.com/CoreWCF/CoreWCF/releases/tag/v1.9.1)
- [https://github.com/CoreWCF/CoreWCF/security/advisories/GHSA-2288-8h3r-cqgg](https://github.com/CoreWCF/CoreWCF/security/advisories/GHSA-2288-8h3r-cqgg)

## Related threats

- [CoreWCF signature verification bypass in WS-Security](https://junglewise.ai/threats/cve-2026-54783-corewcf-signature-verification-bypass-in-ws-security)
- [CoreWCF authentication bypass in SAML token validation](https://junglewise.ai/threats/cve-2026-54782-corewcf-authentication-bypass-in-saml-token-validation)
- [CoreWCF improper authentication in SAML SamlSecurityTokenHandler](https://junglewise.ai/threats/cve-2026-54781-corewcf-improper-authentication-in-saml-samlsecuritytokenhandler)
- [CoreWCF algorithm downgrade in WS-Security receive pipeline](https://junglewise.ai/threats/cve-2026-54780-corewcf-algorithm-downgrade-in-ws-security-receive-pipeline)
- [CoreWCF SAML token replay protection bypass in DefaultTokenReplayCache](https://junglewise.ai/threats/cve-2026-54779-corewcf-saml-token-replay-protection-bypass-in)