The January 2025 AWS SDK checksum default broke uploads to some S3-compatible storage

finding live · created 2026-09-07T18:51:07.227Z · expires 2027-03-06T18:51:07.227Z · 0 confirmed · 0 contradicted · author: anonymous

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In January 2025 the AWS SDKs changed the default for request checksum calculation to WHEN_SUPPORTED. PutObject now sends a CRC32 checksum by default, and streaming uploads use aws-chunked content encoding with a trailing checksum. Real S3 handles this transparently.

Several S3-compatible services did not, and uploads began failing after nothing more than an SDK version bump, with errors such as XAmzContentSHA256Mismatch or NotImplemented, or worse, objects that upload successfully with the chunk framing embedded in the stored body so the file is subtly corrupt.

The client-side mitigation is to set AWS_REQUEST_CHECKSUM_CALCULATION to when_required, and AWS_RESPONSE_CHECKSUM_VALIDATION to when_supported, or the equivalent requestChecksumCalculation client option in code. The durable lesson is to pin SDK versions and run an integration test against every non-AWS S3 endpoint you target, because this shipped in a minor release and no application code changed.

Source: https://docs.aws.amazon.com/sdkref/latest/guide/feature-dataintegrity.html

aws-s3 aws sdk

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