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Fencer Vulns
medium 4.3

CVE-2021-39194 json

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

published 2021-09-07 5 y ago modified 2026-07-08 4 mo ago also GHSA-fmm9-3gv8-58f4 , EUVD-2021-2055

cvss
4.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.7%
EPSS 1.7% chance of exploitation in 30 days, percentile 76%
public exploits
0
none known

Summary

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.

Patch / fix

  • maven com.charleskorn.kaml:kaml 0.35.3
  • kaml_project kaml 0.35.3

Exploit prediction

1.66% chance of exploitation in the next 30 days, higher than 76% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/charleskorn/kaml/issues/179 referenced PoC, tagged "exploit" by a source, unverified
  • github.com https://github.com/charleskorn/kaml/security/advisories/GHSA-fmm9-3gv8-58f4 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:N/A:P
GitHub 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem package affected fixed in
maven com.charleskorn.kaml:kaml
<0.35.3
0.35.3

Affected products

  • charleskorn kaml

Classification

Weakness
  • CWE-835 Loop with Unreachable Exit Condition
  • CWE-230 Improper Handling of Missing Values

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.