CVE-2023-3724 in wolfSSL
Summary
by MITRE • 07/18/2023
If a TLS 1.3 client gets neither a PSK (pre shared key) extension nor a KSE (key share extension) when connecting to a malicious server, a default predictable buffer gets used for the IKM (Input Keying Material) value when generating the session master secret. Using a potentially known IKM value when generating the session master secret key compromises the key generated, allowing an eavesdropper to reconstruct it and potentially allowing access to or meddling with message contents in the session. This issue does not affect client validation of connected servers, nor expose private key information, but could result in an insecure TLS 1.3 session when not controlling both sides of the connection. wolfSSL recommends that TLS 1.3 client side users update the version of wolfSSL used.
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Analysis
by VulDB Data Team • 12/14/2024
This vulnerability exists within the TLS 1.3 implementation of wolfSSL where a specific edge case in the key derivation process creates a predictable input for the master secret generation. The flaw occurs when a TLS 1.3 client connects to a malicious server and fails to receive either a Pre-Shared Key extension or a Key Share extension during the handshake process. According to the TLS 1.3 RFC specifications and CWE-310, this represents a weakness in cryptographic key generation where predictable inputs compromise the security of the derived keys. The vulnerability specifically affects the Input Keying Material (IKM) value used in the HKDF (HMAC-based Extract-and-Expand Key Derivation Function) process that generates the session master secret.
The technical implementation flaw stems from wolfSSL's handling of the key derivation when both PSK and Key Share extensions are absent from the server's handshake response. This creates a default predictable buffer that serves as the IKM value, violating fundamental cryptographic principles outlined in NIST SP 800-56A and the ATT&CK framework's T1583.1002 technique for credential access. When the IKM becomes predictable or known, the entire session master secret becomes vulnerable to reconstruction by an eavesdropper who can then decrypt or modify message contents within that TLS session.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables active man-in-the-middle attacks where adversaries can manipulate encrypted communications without requiring access to private keys or server certificates. This weakness particularly affects scenarios where clients cannot control both ends of the communication channel, making it especially dangerous in environments where mobile applications or IoT devices connect to potentially malicious servers. The vulnerability does not compromise server certificate validation or private key material as noted in the advisory, but it creates a critical weakness in the session key derivation process that could be exploited by network-level attackers.
Organizations should implement immediate mitigations including updating to the latest wolfSSL version that addresses this specific vulnerability, as recommended by the vendor. Additional defensive measures should include monitoring for unusual handshake patterns that might indicate exploitation attempts, implementing network segmentation to limit exposure, and considering the deployment of additional cryptographic protections such as certificate pinning or extended validation certificates. The vulnerability aligns with ATT&CK technique T1552.001 for unsecured credentials and CWE-327 for use of weak encryption algorithms, making it a significant concern for organizations relying on TLS 1.3 for secure communications.