Bithumb, Coinone and Korbit, in addition to four other major exchanges, satisfied investigators during the audit, which took place between September and December 2018.
Of the tranche of 21 platforms involved, however, the remaining 14 failed to meet the criteria for suitable security procedures.
South Korea previously had one of the world’s most active cryptocurrency trading economies before regulatory upheaval saw consumer habits dramatically change in late 2017.
In the interim, attackers have continually targeted South Korean operators in order to steal funds from users, with even officially secure ones such as Bithumb reporting breaches last year worth tens of millions of dollars.
The latest audit by lawmakers looked at 85 different aspects of security, and found that of those who did not pass, an average of 51 aspects required attention, ZDNet reports.
Last month, a court acquitted Bithumb in a case brought by one investor who claimed he lost funds worth $355,000 in a hack because of the platform.
While no mention of shutdowns as a result of poor performance has surfaced, Seoul has been more draconian on certain other aspects of the cryptocurrency industry, with initial coin offerings (ICO) still facing a full ban under its jurisdiction.