Nokogiri is an open source XML and HTML library for the Ruby programming language. Nokogiri 1.13.8 and 1.13.9 fail to check the return value from xmlTextReaderExpand in the method Nokogiri::XML::Reader#attributehash. This can lead to a null pointer exception when invalid markup is being parsed. For applications using XML::Reader to parse untrusted inputs, this may potentially be a vector for a denial of service attack. Users are advised to upgrade to Nokogiri >= 1.13.10. Users may be able to search their code for calls to either XML::Reader#attributes or XML::Reader#attributehash to determine if they are affected.