Downloading a (open-source) DBC is legal. Downloading a leaked proprietary DBC may be illegal depending on your jurisdiction. For example, Tesla has successfully sued individuals distributing their DBCs.
: Used in heavy-duty vehicles, these files are often sold through resellers like CSS Electronics or Tecnologix as they contain thousands of PGNs and SPNs defined by the SAE. can dbc file download
While the file format itself was created by Vector Informatik GmbH and is a de facto industry standard, the content within most DBC files is highly guarded intellectual property. : Downloading a (open-source) DBC is legal