CoreWCF SPNEGO SecurityContextToken Proof Key Exposure

Executive Summary

This vulnerability exists in CoreWCF version 1.9.0, which is a port of the Windows Communication Foundation to .NET Core. It involves the SPNEGO SecurityContextToken negotiation process. Specifically, when using TransportWithMessageCredential with Windows client credentials and session establishment, the proof key recovered from the RSTR message can be exposed. This exposure allows an observer to impersonate the authenticated Windows principal and to decrypt or forge WS-SecureConversation traffic.

The issue is resolved in CoreWCF version 1.9.1.

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Impact Analysis

This vulnerability can have serious security impacts. An attacker who observes the exposed proof key can impersonate an authenticated Windows user, gaining unauthorized access to systems or data. Additionally, the attacker can decrypt or forge WS-SecureConversation traffic, potentially leading to data breaches, unauthorized data manipulation, or further attacks within the affected communication sessions.

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Mitigation Strategies

To mitigate this vulnerability, upgrade CoreWCF to version 1.9.1 or later, where the issue has been fixed.

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Compliance Impact

The vulnerability exposes sensitive security tokens and keys in cleartext over the network, allowing an attacker to impersonate authenticated users and decrypt or forge secure conversation traffic. This exposure of sensitive data in transit can lead to violations of data protection requirements found in common standards and regulations such as GDPR and HIPAA, which mandate the protection of personal and sensitive information during transmission.

Specifically, the vulnerability relates to missing encryption of sensitive data (CWE-311) and unprotected transport of credentials (CWE-523), both of which are critical concerns under these regulations. Without proper encryption, the confidentiality and integrity of protected data are compromised, potentially resulting in non-compliance with regulatory requirements for secure data handling and transmission.

Mitigation involves applying the patch in CoreWCF version 1.9.1 or ensuring SSL/TLS protection to prevent attackers from capturing the negotiation handshake, thereby helping maintain compliance with these standards.

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Detection Guidance

This vulnerability involves the exposure of the SPNEGO SecurityContextToken proof key in the WS-Trust RSTR response when TransportWithMessageCredential with Windows client credentials and session establishment are used without proper encryption.

To detect this vulnerability on your network or system, you should monitor WS-Trust RSTR messages for the presence of base64-encoded proof keys that are not encrypted (i.e., visible in cleartext). This can be done by capturing network traffic on non-TLS connections where CoreWCF 1.9.0 or earlier is in use.

Suggested commands include using network packet capture tools such as tcpdump or Wireshark to capture and inspect the WS-Trust RSTR messages for unencrypted proof keys.

• Use tcpdump to capture traffic on the relevant port (e.g., port 80 or other non-TLS ports): tcpdump -i <interface> -w capture.pcap
• Open the capture in Wireshark and filter for WS-Trust RSTR messages or SOAP messages containing the RequestedProofToken element.
• Inspect the RequestedProofToken for base64-encoded data that appears in cleartext, indicating the proof key is not encrypted.

If you observe unencrypted proof keys in the RSTR messages, your system is vulnerable. Upgrading to CoreWCF version 1.9.1 or later is recommended to fix this issue.

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