A user in the UK told the Sun newspaper earlier this week her Samsung device could be unlocked by someone else simply by putting on a screen protector and applying an unregistered fingerprint.
"This means that if anyone got hold of my phone they can access it and within moments could be into the financial apps and be transferring funds," she was quoted as saying by the British paper.
Samsung's spokesperson in Seoul said the company will soon roll out a fix, but did not say what caused the recognition problem.
"We are investigating this issue and will be deploying a software patch soon," she told AFP.
The world's biggest smartphone maker has touted the phone's in-display fingerprint sensor as "revolutionary".
"When you place your thumb on the screen, it sends ultrasonic pulses to detect the 3D ridges and valleys of your unique fingerprint to quickly and accurately recognise you," the firm has said about the specific technology.
Kakaobank, South Korea's internet-only bank, has told its customers to use passwords and pattern locks when using its mobile banking services until the problem is fixed.
Samsung is the flagship subsidiary of the giant Samsung Group, by far the biggest of the family-controlled conglomerates that dominate business in the world's 11th-largest economy, and crucial to South Korea's economic health.
But it has a history of humiliating setbacks with major products, most notably a worldwide recall of its Galaxy Note 7 devices in 2016 over exploding batteries, which hammered its reputation.
Its first foldable smartphone, the Galaxy Fold, was launched last month months after faulty screens forced an embarrassing delay of its release.
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