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CoreWCF: SPNEGO SecurityContextToken proof key wrapped without confidentiality

High severity GitHub Reviewed Published Jun 16, 2026 in CoreWCF/CoreWCF • Updated Jun 19, 2026

Package

nuget CoreWCF.Primitives (NuGet)

Affected versions

>= 1.9.0, < 1.9.1

Patched versions

1.9.1

Description

Impact

When the proof key recovered from the RSTR can be observed by a party that is not the legitimate client, that party can impersonate the authenticated Windows principal for the lifetime of the SCT (default ~10 hours) and decrypt or forge any subsequent WS‑SecureConversation traffic that uses keys derived from the SCT.

Preconditions

Using security mode TransportWithMessageCredential with client credential type Windows, along with session establishment (which triggers use of WS-SecureConversation).

Patches

Fixed in CoreWCF v1.9.1

Workarounds

Ensure communication is protected by SSL/TLS to prevent capturing of SCT negotiation handshake.

References

@mconnew mconnew published to CoreWCF/CoreWCF Jun 16, 2026
Published to the GitHub Advisory Database Jun 19, 2026
Reviewed Jun 19, 2026
Last updated Jun 19, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(19th percentile)

Weaknesses

Missing Encryption of Sensitive Data

The product does not encrypt sensitive or critical information before storage or transmission. Learn more on MITRE.

Unprotected Transport of Credentials

Login pages do not use adequate measures to protect the user name and password while they are in transit from the client to the server. Learn more on MITRE.

CVE ID

CVE-2026-54784

GHSA ID

GHSA-2288-8h3r-cqgg

Source code

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