CVE-2025-66016 identifies a critical cryptographic vulnerability in the LFDT-Lockness cggmp21 product, which implements the CGGMP24 ECDSA threshold signature scheme (TSS). This protocol supports efficient signing with one round of signing after three preprocessing rounds, identifiable aborts, and key refresh capabilities. The vulnerability arises from an insufficient verification step in the zero-knowledge proof mechanism prior to version 0.6.3. Specifically, the protocol fails to adequately verify the authenticity of data in the ZK proof, classified under CWE-345 (Insufficient Verification of Data Authenticity). This flaw enables a single malicious participant (signer) within the threshold signature scheme to reconstruct the entire private key, thereby breaking the fundamental security guarantees of the cryptographic system. The attack does not require any authentication or user interaction and can be executed remotely, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N). The impact on confidentiality and integrity is high, as the private key compromise can lead to unauthorized signature generation, impersonation, and data breaches. The vulnerability was patched in version 0.6.3, with further security enhancements in version 0.7.0-alpha.2. No known exploits have been reported in the wild, but the critical nature of the flaw demands immediate attention. The vulnerability affects all deployments using cggmp21 versions earlier than 0.6.3, particularly those relying on threshold ECDSA for secure multi-party signing operations.

The potential impact on European organizations is severe due to the critical nature of the vulnerability. Organizations using cggmp21 in cryptographic operations risk full private key compromise, which can lead to unauthorized transaction signing, data integrity violations, and loss of trust in digital signatures. This is especially impactful for sectors such as banking, finance, telecommunications, government, and critical infrastructure, where threshold signatures are used to secure sensitive operations and multi-party authorization. The compromise of private keys could facilitate fraud, unauthorized access, and disruption of services. Additionally, the breach of cryptographic keys may have regulatory implications under GDPR and other European cybersecurity laws, potentially resulting in fines and reputational damage. The lack of known exploits in the wild does not diminish the urgency, as the vulnerability is straightforward to exploit by a malicious insider or attacker with access to the signing process. The scope of affected systems includes any cryptographic infrastructure leveraging vulnerable versions of cggmp21, which may be embedded in hardware security modules (HSMs), blockchain platforms, or secure communication systems.

To mitigate this vulnerability, European organizations should immediately upgrade all instances of the LFDT-Lockness cggmp21 product to version 0.6.3 or later, with a strong recommendation to adopt version 0.7.0-alpha.2, which includes additional security checks. Organizations should audit their cryptographic implementations to identify any use of vulnerable versions and verify that no unauthorized key reconstruction has occurred. Implement strict access controls and monitoring around signing operations to detect anomalous behavior indicative of an insider threat. Where possible, employ hardware-based security modules that enforce cryptographic operations and prevent key extraction. Additionally, organizations should review their multi-party signing protocols to ensure no single participant can compromise the entire key. Regularly update threat intelligence and vulnerability management processes to detect and respond to emerging exploits. Finally, consider engaging with vendors and cryptographic experts to validate the security posture of threshold signature deployments and apply best practices for key management and protocol verification.