Ktor
CVE-2021-43203
HIGH
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A07:2025 - Authentication Failures
ASVS 5.0
V6 - Authentication Authentication mechanism validation
MITRE ATT&CK
2 techniques across 2 tactics: Defense Evasion, Initial Access The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS score of 7.5 (HIGH). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required. |
| Exploit ScenarioDerived | A remote attacker could bypass authentication mechanisms to gain unauthorized access by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability. |
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Alert meAnalysisAI
In JetBrains Ktor before 1.6.4, nonce verification during the OAuth2 authentication process is implemented improperly. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
RemediationAI
No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Implement multi-factor authentication, enforce strong password policies, use proven authentication frameworks.
Affects your stack
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Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This vulnerability is classified as Improper Authentication (CWE-287), which allows attackers to bypass authentication mechanisms to gain unauthorized access. In JetBrains Ktor before 1.6.4, nonce verification during the OAuth2 authentication process is implemented improperly. Affected products include: Jetbrains Ktor. Version information: before 1.6.4.
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionNVD
In JetBrains Ktor before 1.6.4, nonce verification during the OAuth2 authentication process is implemented improperly.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.
Affected Products (CPE)NVD
In Ktor through 1.2.6, the client resends data from the HTTP Authorization header to a redirect location. Rated medium s
In JetBrains Ktor before 2.3.5 default configuration of ContentNegotiation with XML format was vulnerable to XXE. Rated
JetBrains Ktor framework before 1.2.0-rc does not sanitize the username provided by the user for the LDAP protocol, lead
JetBrains Ktor framework before version 1.2.6 was vulnerable to HTTP Response Splitting. Rated medium severity (CVSS 5.4
In JetBrains Ktor before 2.3.5 server certificates were not verified. Rated critical severity (CVSS 9.1), this vulnerabi
JetBrains Ktor framework (created using the Kotlin IDE template) versions before 1.1.0 were resolving artifacts using an
In Ktor before 1.3.0, request smuggling is possible when running behind a proxy that doesn't handle Content-Length and T
In JetBrains Ktor before 2.1.0 the wrong authentication provider could be selected in some cases. Rated medium severity
In JetBrains Ktor before 1.4.1, HTTP request smuggling was possible. Rated medium severity (CVSS 6.5), this vulnerabilit
JetBrains Ktor before 2.1.0 was vulnerable to the Reflect File Download attack. Rated medium severity (CVSS 6.1), this v
In JetBrains Ktor before 3.1.1 an HTTP Request Smuggling was possible. Rated medium severity (CVSS 5.3), this vulnerabil
In JetBrains Ktor before 2.3.13 improper caching in HttpCache Plugin could lead to response information disclosure. Rate
GitHub PoC
Exploit-DB