CVE-2021-39194

Denial of service while parsing polymorphic input with tagged polymorphism style in kaml

MEDIUM
6.5
CVSS Score
Published: September 7, 2021 at 07:25 PM UTC
Updated: June 17, 2026 at 04:03 AM UTC
2 products affected across 2 vendorsKamlProject Kaml

Using kaml by charleskorn?

Get instant alerts when new vulnerabilities affect kaml - before attackers find them.

Real-time alertsTrack your software stackFree plan available
Severity
MEDIUM6.5
Exploit prediction
EPSS 2%

Description

kaml is an open source implementation of the YAML format with support for kotlinx.serialization. In affected versions attackers that could provide arbitrary YAML input to an application that uses kaml could cause the application to endlessly loop while parsing the input. This could result in resource starvation and denial of service. This only affects applications that use polymorphic serialization with the default tagged polymorphism style. Applications using the property polymorphism style are not affected. YAML input for a polymorphic type that provided a tag but no value for the object would trigger the issue. Version 0.35.3 or later contain the fix for this issue.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 0.35.3
Affected range stops below 0.35.3, so it looks safe — our inference, not a vendor statement
v < 0.35.2
Affected range stops below 0.35.2, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

References (3)

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-835

Get alerted

Stop reading CVE feeds looking for your own stack

Track the products you run and VulnTracker tells you when a new CVE affects them — with what is known about fixing it, and nothing about the rest.

Free plan, no card