OpenSSL Encrypt Plaintext Hash Disclosure in File Metadata

Executive Summary

CVE-2026-81688 affects openssl_encrypt versions before 1.4.9. It stores an unkeyed SHA-256 hash of the plaintext in the encrypted file header. Attackers can read this hash without the password to confirm guessed plaintexts offline or identify identical plaintexts across different encrypted files.

Useful 0 Not Useful 0

Detection Guidance

To detect this vulnerability, inspect encrypted files created with openssl_encrypt versions before 1.4.9 for a SHA-256 hash in the header metadata. Use tools like hexdump or file inspection commands to check for unexpected hash storage in file headers.

Useful 0 Not Useful 0

Impact Analysis

Attackers could exploit this to verify guessed plaintexts without the password, potentially exposing sensitive data. It also allows fingerprinting identical plaintexts across multiple encrypted files, increasing the risk of data leaks or unauthorized access.

Useful 0 Not Useful 0

Compliance Impact

This vulnerability may violate data protection requirements under GDPR and HIPAA by failing to adequately protect sensitive data. Storing unkeyed hashes of plaintext undermines encryption best practices, potentially leading to non-compliance with confidentiality and integrity controls.

Useful 0 Not Useful 0

Mitigation Strategies

Upgrade openssl_encrypt to version 1.4.9 or later to remove the unkeyed hash storage. Ensure all encrypted files are re-encrypted with the updated version to prevent hash-based plaintext confirmation attacks.

Useful 0 Not Useful 0