set limits on the maximum size of entities.Д«elow is an example of settings in which the DTD processing is allowed, but the maximum size of entities is limited: XmlReaderSettings settings = new XmlReaderSettings().

'ProhibitDtd' must have the 'true' value to prohibit the DTD processing. NET Framework versions, the 'ProhibitDtd' property is used instead of 'DtdProcessing'.

prohibit or ignore DTD processing - set the 'Prohibit' / 'Ignore' value for the 'DtdProcessing' property.

If we want to make a parser resistant to XEE attacks, we can: The analyzer detects a combination of these factors and issues a warning. Note that the processed data comes from an external source - they are read from the file along 'pathToXml'. The 'MaxCharactersFromEntities' property is set to 0.ДЄs a result, the parser may freeze trying to parse an XML bomb and start consuming a large amount of memory.

the developer didn't set limits on the size of entities.

The 'DtdProcessing' property has the 'DtdProcessing.Parse' value However, this parser is vulnerable to XML bombs because it was created with insecure settings, where: In this example, the 'reader' object parses an XML file. Using (var reader = XmlReader.Create(xml, settings))

Using (var xml = File.OpenRead(pathToXml)) XmlReaderSettings settings = new XmlReaderSettings() Look at the example: static void XEETarget(String pathToXml) You can read about a real-world example of an application vulnerability to XEE in the article: ' How Visual Studio 2022 ate up 100 GB of memory and what XML bombs had to do with it'. an XML parser that processes this file has an insecure configuration.an attacker can pass an XML bomb to an application.Thus, a hacker can perform a DoS attack with XML bombs if: billion laughs (because of a multiple repetition of 'lol').That's where this type of attack got its name: XML bombs are small files that enlarge when entities are expanded. So-called XML bombs are created in a similar way, by increasing the number of nested entities. Lollollollollollollollollollollollollollollollollollollollollollollol The 'lol2' entity expands as follows: lollollollollollollollollollollollollollollollollollollollollollollol We can increase the nesting and the number of entities. The value of the 'lol1' entity results in the 'lollol' string. We define the first one through a string, and the second one through other entities.

The file contains the 'lol' and 'lol1' entities. In the latter case, they can be represented by a string or other entities, for example.ДЄn XML file with examples of such entities: Entities can either refer to some external resource or be fully defined inside the document. DTD allows us to define and use XML entities. XML files may contain the document type definition ( DTD). XEE attacks are included in OWASP Top 10 2017: A4:2017 вЂ“ XML External Entities (XXE), and OWASP Top 10 2021: A05:2021 вЂ“ Security Misconfiguration. This can make an application vulnerable to an XEE attack (also called a 'billion laughs' attack or an XML bombs attack). The analyzer has detected the use of an insecurely configured XML parser that processes external data.

Xee definition