CVE-2021-43203: JetBrains Ktor

High severity, CVSS 7.5. EPSS: 0.9% chance of exploitation in the next 30 days.

In JetBrains Ktor before 1.6.4, nonce verification during the OAuth2 authentication process is implemented improperly.

Affected products

• JetBrains Ktor: before 1.6.4 (fixed in 1.6.4)

Published 2021-11-09. Last modified 2026-06-17.