Plaintext substitution via uncommitted encrypted data keys

Missing key commitment in the AWS SDK for PHP S3 Encryption Client before 3.368.0 allows remote authenticated users to substitute object plaintext. When an encrypted data key is stored in an instruction file, the client accepts a replacement EDK without cryptographically binding it to the ciphertext, so later decryption can yield attacker-selected plaintext. Exploitation requires S3 bucket write access, a separately crafted rogue EDK, and use of instruction files rather than S3 object metadata; it alters decrypted content without exposing or interrupting the service.