Ceph RGW: unsigned x-amz-* headers on presigned URLs are honored, letting a URL holder escalate privileges

Impact

RGW validates only the headers listed in X-Amz-SignedHeaders and ignores any additional x-amz-* headers, unlike S3 which rejects them. Anyone holding a presigned URL can attach unsigned x-amz-* headers that RGW acts on, obtaining capabilities the signer never intended to delegate - a presigned PUT becomes a lever for more than the single scoped write. On a GPU fleet this matters because Ceph RGW is commonly the shared bucket layer for datasets, checkpoints and model artifacts across tenants, and presigned URLs are routinely handed to training jobs, notebooks and external collaborators as a deliberately narrow grant. The record scores it 8.1 with confidentiality and integrity impact and no availability impact.

Who can reach it

Anyone who has been given a presigned RGW URL, including a party with no account on the cluster. No further authentication is needed - the presigned URL itself is the credential, and the attacker only needs network reach to the RGW endpoint.

What to do

Upgrade Ceph to 20.2.4 or 19.2.6, which the advisory names as the fixed releases, and restart the radosgw daemons; no OSD or MON restart is implied by the fix and client I/O to the gateway is interrupted only for the rolling restart window. Until you can upgrade, treat outstanding presigned URLs as broader grants than intended - shorten their expiry and reissue anything long-lived. The advisory does not describe a configuration-level mitigation that leaves the gateway in service.

References

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