CVE-2025-54885 is a vulnerability in the simbo1905 thinbus-srp-npm package, which implements the Secure Remote Password protocol version 6a (SRP6a) in JavaScript for browser-based zero-knowledge password authentication. The vulnerability arises from a protocol compliance bug in versions 2.0.0 and below, where the client generates a private value with insufficient entropy—specifically, only 252 bits instead of the intended 2048 bits corresponding to the safe prime size. This reduction occurs because the private value is generated 4 bits below the specification, significantly weakening the cryptographic strength of the client’s public value. As a result, the security margin designed into the SRP protocol is compromised, making it practically exploitable by attackers who can leverage the reduced entropy to perform offline attacks or recover session keys. The server side continues to use a full 2048-bit random number to generate the shared session key and password proof, but the client-side weakness undermines the overall protocol security. This flaw is addressed in version 2.0.1 of thinbus-srp-npm, which restores proper entropy generation. The CVSS 4.0 base score is 6.9 (medium severity), reflecting network attack vector, high attack complexity, no privileges or user interaction required, but with high impact on confidentiality and integrity. No known exploits are reported in the wild as of the publication date.

For European organizations, this vulnerability poses a significant risk to any web applications or services that rely on thinbus-srp-npm versions prior to 2.0.1 for secure password authentication. The reduced entropy in the client’s private value can allow attackers to compromise authentication sessions, potentially leading to unauthorized access, credential compromise, and session hijacking. This undermines the confidentiality and integrity of user credentials and session data. Organizations handling sensitive personal data, financial information, or critical infrastructure access are particularly at risk, as exploitation could facilitate further lateral movement or data breaches. Given the widespread adoption of JavaScript-based authentication libraries in web applications, the vulnerability could affect a broad range of sectors including finance, healthcare, government, and e-commerce within Europe. The medium severity rating suggests that while exploitation is not trivial, the impact on affected systems could be substantial if exploited. The lack of known exploits currently provides a window for proactive mitigation.

European organizations should immediately audit their software dependencies to identify usage of thinbus-srp-npm versions below 2.0.1. Upgrading to version 2.0.1 or later is the primary and most effective mitigation, as it corrects the entropy generation flaw. For applications where immediate upgrade is not feasible, organizations should consider implementing compensating controls such as additional multi-factor authentication layers to reduce the risk of compromised credentials. Monitoring authentication logs for unusual patterns or repeated failed attempts can help detect exploitation attempts. Developers should review their implementation of SRP protocols to ensure compliance with specifications and proper entropy sources. Additionally, organizations should conduct penetration testing focused on authentication mechanisms to validate the effectiveness of mitigations. Finally, educating development teams about cryptographic best practices and the importance of using well-maintained libraries can prevent similar issues.