Security Disclosure: Improper validation of configured threshold for delegations

Summary

A compromised or misconfigured TUF repository can have the configured value of signature thresholds set to 0, which effectively disables signature verification.

Impact

Unathorized modification to TUF metadata files is possible at rest, or during transit as no integrity checks are made.

Patches

Upgrade to v2.3.1

Workarounds

Always make sure that the TUF metadata roles are configured with a threshold of at least 1.

Affected code:

The metadata.VerifyDelegate did not verify the configured threshold prior to comparison. This means that a misconfigured TUF repository could disable the signature verification by setting the threshold to 0, or a negative value (and so always make the signature threshold computation to pass).