In AWS SDK for PHPv3.337.0, we released changes to the S3 client that adopts new default integrity protections. For more information on default integrity behavior, please refer to the officialSDK documentation. In SDK releases from this version on, clients default to enabling an additional checksum on all Put calls and enabling validation on Get calls.

You can disable default integrity protections for S3. We do not recommend this because checksums are important to S3 integrity posture. Integrity protections can be disabled by setting the config flag toWHEN_REQUIRED, or by using the related AWS shared config file settings or environment variables.

Disclaimer: the AWS SDKs and CLI are designed for usage with official AWS services. We may introduce and enable new features by default, such as these newdefault integrity protections, prior to them being supported or otherwise handled by third-party service implementations. You can disable the new behavior with theWHEN_REQUIRED value for therequest_checksum_calculation andresponse_checksum_validation configuration options covered inData Integrity Protections for Amazon S3.