CVE-2021-39194: Denial of service while parsing polymorphic input with tagged polymorphism style in kaml

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.7% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-09-07 · updated 2026-06-17
Weakness: CWE-835

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 products

charleskorn kaml: before 0.35.3 — fixed in 0.35.3

How to fix

Upgrade to a fixed version: charleskorn kaml 0.35.3. Check the vendor advisory for mitigations.

References

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