The vulnerability identified as CVE-2026-23966 affects the sm-crypto JavaScript library developed by JuneAndGreen, which provides implementations of Chinese cryptographic algorithms SM2 (asymmetric encryption), SM3 (hashing), and SM4 (symmetric encryption). Specifically, the flaw lies in the SM2 decryption logic in versions prior to 0.3.14. SM2 is widely used in Chinese cryptographic standards for public key encryption and digital signatures. The vulnerability is categorized under CWE-345, indicating insufficient verification of data authenticity. An attacker can exploit this by repeatedly interacting with the SM2 decryption interface, performing several hundred decryption operations to recover the private key fully. This private key recovery enables the attacker to decrypt confidential data, forge signatures, and impersonate legitimate users or services. The vulnerability is remotely exploitable without requiring privileges or user interaction, making it highly dangerous. The CVSS v3.1 score of 9.1 reflects its critical severity, with high impact on confidentiality and integrity but no impact on availability. Although no known exploits are reported in the wild yet, the ease of exploitation and severity warrant immediate attention. The patch was released in version 0.3.14, which corrects the decryption logic to prevent private key leakage.

For European organizations, the impact of this vulnerability can be severe if sm-crypto is used in applications that handle sensitive or regulated data, especially in sectors such as finance, telecommunications, or government services that may rely on Chinese cryptographic standards for compliance or interoperability. The private key recovery allows attackers to decrypt confidential communications, manipulate data integrity, and potentially conduct identity theft or fraud. This can lead to data breaches, regulatory penalties under GDPR, loss of customer trust, and disruption of secure communications. The vulnerability's remote exploitability without authentication increases the risk of widespread attacks. Organizations using sm-crypto in client-side or server-side JavaScript environments are particularly vulnerable. Additionally, supply chain risks exist if third-party software or services incorporate vulnerable versions of sm-crypto. The lack of known exploits in the wild currently provides a window for mitigation, but the critical nature demands prompt action.

1. Immediately upgrade all instances of sm-crypto to version 0.3.14 or later to apply the patch that fixes the private key recovery vulnerability. 2. Conduct a thorough audit of all applications and services using sm-crypto to identify affected versions and usage contexts. 3. Replace or rotate any private keys that may have been exposed due to this vulnerability, especially if the vulnerable versions were in use in production environments. 4. Implement strict access controls and monitoring on cryptographic key usage to detect abnormal decryption request patterns that could indicate exploitation attempts. 5. Where possible, consider migrating to more widely vetted cryptographic libraries that implement SM2, SM3, and SM4 with proven security records. 6. Educate developers and security teams about the risks of using cryptographic libraries with insufficient data authenticity verification. 7. Monitor threat intelligence sources for any emerging exploits targeting this vulnerability. 8. For critical systems, consider additional cryptographic safeguards such as hardware security modules (HSMs) to protect private keys from software-level attacks.