Package Instance

Clarify Content-Type handling
### Impact
In the OCI Distribution Specification version 1.0.0 and prior, the Content-Type header alone was used to determine the type of document during push and pull operations. Documents that contain both “manifests” and “layers” fields could be interpreted as either a manifest or an index in the absence of an accompanying Content-Type header. If a Content-Type header changed between two pulls of the same digest, a client may interpret the resulting content differently.

### Patches
The OCI Distribution Specification will be updated to require that a `mediaType` value present in a manifest or index match the Content-Type header used during the push and pull operations.

### Workarounds
Clients pulling from a registry may distrust the Content-Type header and reject an ambiguous document that contains both “manifests” and “layers” fields or “manifests” and “config” fields.

### References
https://github.com/opencontainers/image-spec/security/advisories/GHSA-77vh-xpmg-72qh

### For more information
If you have any questions or comments about this advisory:
* Open an issue in https://github.com/opencontainers/distribution-spec/
* Email us at security@opencontainers.org