CVE-2025-6547 identifies a critical improper input validation vulnerability in the pbkdf2 npm package that enables attackers to exploit cryptographic key derivation weaknesses by causing the library to silently disregard Uint8Array input on historic Node.js versions, resulting in static predictable keys being generated instead of cryptographically secure outputs. This vulnerability affects pbkdf2 versions up to 3.1.2 when running on Node.js versions prior to 3.0.0, achieving a CVSS score of 9.1 (Critical severity) with EPSS percentile of 28.6 indicating extremely high exploit risk for legacy JavaScript applications and older Node.js environments utilizing pbkdf2 for cryptographic key derivation with Uint8Array input types. The vulnerability details reveal that inadequate type checking and conversion mechanisms in the toBuffer utility function cause Uint8Array inputs to be treated as empty strings during key derivation operations, enabling attackers to predict generated keys since they consistently produce the same static hash output equivalent to processing empty password and salt values, creating substantial exploit risk for applications relying on pbkdf2 for secure key generation in authentication systems, password storage, and cryptographic protocols. The root cause analysis reveals that the vulnerability stems from flawed type-checking implementation in the lib/to-buffer.js utility function where inadequate Uint8Array conversion handling causes cryptographic inputs to be processed as empty values during key derivation, classified as CWE-20 (Improper Input Validation). The vulnerability specifically affects pbkdf2 and pbkdf2Sync functions where the toBuffer utility fails to correctly convert Uint8Array inputs into proper Buffer objects on Node.js versions below 3.0.0, enabling attackers to exploit known exploited vulnerabilities targeting cryptographic key predictability to compromise applications that unknowingly generate static keys for sensitive operations including password hashing and authentication tokens. Mitigation steps require immediate upgrading to pbkdf2 version 3.1.3 or later which implements proper Uint8Array handling through external to-buffer dependency that correctly processes typed array inputs, followed by comprehensive security audits to identify and regenerate any compromised keys that may have been generated using Uint8Array inputs on affected Node.js versions. Organizations should prioritize identifying JavaScript applications using vulnerable pbkdf2 versions on legacy Node.js environments, audit all previously generated cryptographic keys for potential static key compromise especially those using Uint8Array input formats, implement strict input type validation before key derivation operations, consider migrating from legacy Node.js versions to modern runtime environments with proper typed array support, and maintain updated vulnerability database records to track similar cryptographic input validation vulnerabilities that could compromise application security through predictable key generation and broader security implications for legacy JavaScript environments with insufficient type handling controls in cryptographic libraries.