The claim was made by researchers at US security firm Recorded Future who had initially pointed out the difference in speed of publishing between the Chinese database and its US counterpart, the US National Vulnerability Database (NVD).
They had found that NVD trailed the CNNVD in the time taken between initial disclosure of a flaw and its inclusion in the database – while the NVD took an average of 33 days, the CNNVD took just 13.
But later they found that this did not apply to more serious vulnerabilities and theorised that this could be because publication was being delayed to allow time to evaluate how they could be used in domestic surveillance.
In a blog post, Dr Ladd and Priscilla Moriuchi said during their initial study, back in November 2017, they had also found that the CNNVD was essentially a shell for the Ministry of State Security.
"This is important because the MSS is not just a foreign intelligence service, but it also has a large, and arguably more important, domestic intelligence mandate," they wrote.
"Recognising the importance of the domestic mission is key to understanding why the MSS would manipulate data that is primarily consumed by Chinese or regional users."
The motive for altering dates was to prevent Chinese researchers from finding details of a vulnerability in the event that it was being used for an attack within China.
"For example, if a company was victimised by an exploit for CVE-2017-0199 on May 15, 2017 and used CNNVD data, then it would not have known to remediate that vulnerability until June 7, 2017," Ladd and Moriuchi wrote.
"Since CNNVD altered the publication date for this vulnerability after publication to April 13, 2017, a current examination of the vulnerability could lead investigators to conclude that the company was aware of the vulnerability after April 13 but chose not to remediate.
"Depending upon the data loss, the breach, and the country, this data manipulation could put companies at further risk for fines or legal action resulting from an intrusion."