Upvote:2
According to Timatic, the system used by airlines, transiting without a visa is possible for:
Passengers transiting through Seoul (ICN) with a confirmed onward ticket for a flight to a third country within 24 hours. They must stay in the international transit area of the airport and have documents required for the next destination.
Passengers with a confirmed onward ticket for a flight to a third country on the same calendar day. They must stay in the international transit area of the airport and have documents required for the next destination.
Source: https://www.timaticweb2.com/integration/external.php?ref=d975cfc59f5c0abd06d16e872198110b