openssl_encrypt versions before 1.4.9 derive the remote-pepper wrap key using unsalted HKDF-SHA256 or bare SHA-256 of the password, allowing identical keys across all users and files. Attackers with access to wrapped pepper blobs can precompute a single dictionary table and perform fleet-wide offline password guessing at hardware speed to recover user passwords.

CVE-2026-81689 affects openssl_encrypt versions before 1.4.9, which derive the remote-pepper wrap key using unsalted HKDF-SHA256 or bare SHA-256 of the password. This flawed key derivation results in identical keys being generated across all users and files, eliminating the security benefit of per-user uniqueness. Attackers who gain access to wrapped pepper blobs can precompute a single dictionary/rainbow table and apply it fleet-wide. This enables offline password guessing attacks at hardware speed, dramatically accelerating credential recovery. The vulnerability effectively undermines the password protection mechanism for all users of affected versions. The fix is available in version 1.4.9 and later. The issue is documented in the GitHub security advisory GHSA-3v63-778v-3mvp and VulnCheck advisories. Organizations using openssl_encrypt should upgrade immediately to mitigate the risk of mass password compromise.