CVE-2021-43203

Name: CVE-2021-43203
Creator: NVD / NIST
Published: 2021-11-09T15:15:10.11+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 0.84%

Last modified Jun 17, 2026

CVE-2021-43203 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. In JetBrains Ktor before 1.6.4, nonce verification during the OAuth2 authentication process is implemented improperly.. EPSS estimates a 0.84% chance of exploitation in the next 30 days.

Description

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

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Probability

0.84%

53.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-287

Affected Software

Vendor	Product	Versions
Jetbrains	Ktor	< 1.6.4

References

https://blog.jetbrains.com/blog/2021/11/08/jetbrains-security-bulletin-q3-2021/Vendor Advisory
https://blog.jetbrains.com/blog/2021/11/08/jetbrains-security-bulletin-q3-2021/Vendor Advisory

Timeline

Published: Nov 9, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-43203?

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

How severe is CVE-2021-43203?

CVE-2021-43203 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.84% probability of exploitation in the next 30 days.

How do I fix CVE-2021-43203?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-43203?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST