The CheckRedirect policy stripped only the X-Amz-Security-Token header when a
redirect crossed a host, leaving other origin-bound secrets exposed:
- Go removes Authorization on a hostname change but not on a same-host scheme
downgrade, so an IBM IAM bearer token was re-sent over plaintext HTTP.
- The SSE-C and copy-source SSE-C customer-key headers (which Go has no reason
to treat as sensitive) were forwarded across a redirect to another host.
- On a cross-host redirect net/http copies the previous request URL into the
Referer header; for a presigned request that URL carries the signature and
session token in its query string, disclosing them to the new origin.
This now refuses outright to follow any HTTPS->HTTP redirect - an S3 endpoint
has no legitimate reason to downgrade the transport, and this closes the
plaintext-exposure class regardless of which header or query string carries the
secret. On a cross-host redirect also strip the known credential headers and the
Referer.
The IDrive e2 region-lookup call posts the access key ID to a fixed HTTPS
endpoint but used a bare http.Client that would follow a redirect downgrading
to plaintext HTTP. Apply the same CheckRedirect policy as the main S3 client so
the request can't be replayed over an unencrypted connection.
Fixes GHSA-8mxv-9xhp-86h4
Nick Craig-Wood
9328763d1b