A solução mais curta jq
:
jq -sc 'group_by(.vulnid)[] | add' file*.json
A saída:
{"vulnid":"cve1","product":"product1","version":"version1","patch":"patch1","speed":"speed1"}
{"vulnid":"cve2","product":"product2","version":"version2","patch":"patch2","power":"power2"}
{"vulnid":"cve3","product":"product3","version":"version3","patch":"patch3","amps":"amps3"}
{"vulnid":"cve4","product":"product4","version":"version4","patch":"patch4"}
{"vulnid":"cve5","product":""}
{"vulnid":"cve6","product":""}