Ecosyste.ms: Advisories

Security Advisories: GSA_kwCzR0hTQS1mbW05LTNndjgtNThmNM0Vng

Improper Handling of Missing Values in kaml

Impact

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, 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")
}

On vulnerable versions of kaml, the decodeFromString() operation hangs and never returns.

Patches

Version 0.35.3 or later contain the fix for this issue.

Permalink: https://github.com/advisories/GHSA-fmm9-3gv8-58f4
JSON: https://advisories.ecosyste.ms/api/v1/advisories/GSA_kwCzR0hTQS1mbW05LTNndjgtNThmNM0Vng
Source: GitHub Advisory Database
Origin: Unspecified
Severity: Moderate
Classification: General
Published: over 3 years ago
Updated: almost 2 years ago

CVSS Score: 4.3
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

EPSS Percentage: 0.00132
EPSS Percentile: 0.48805

Identifiers: GHSA-fmm9-3gv8-58f4, CVE-2021-39194
References:

• https://github.com/charleskorn/kaml/security/advisories/GHSA-fmm9-3gv8-58f4
• https://github.com/charleskorn/kaml/issues/179
• https://github.com/charleskorn/kaml/commit/e18785d043fc6324c81e968aae9764b4b060bc6a
• https://nvd.nist.gov/vuln/detail/CVE-2021-39194
• https://github.com/advisories/GHSA-fmm9-3gv8-58f4

Repository: https://github.com/charleskorn/kaml
Blast Radius: 9.6

Affected Packages