kaml has potential denial of service while parsing input with anchors and aliases

Impact

Applications that use kaml to parse untrusted input containing anchors and aliases may consume excessive memory and crash.

Patches

Version 0.53.0 and later default to refusing to parse YAML documents containing anchors and aliases.

Workarounds

None.

References

Wikipedia has an explanation of this class of vulnerability: billion laughs attack

Acknowledgements

Thank you to @gdude2002 for reporting this issue.