CVE-2021-27918: Vulnerability in golang - Infinite Loop in encoding/xml

Background

The golang package is a popular open-source programming language that provides a robust set of tools and libraries for building efficient and reliable applications. It is widely used for developing various types of software, including web applications, network servers, and command-line tools. The encoding/xml package in golang is responsible for encoding and decoding XML data. It provides functions like xml.NewTokenDecoder, Decode, DecodeElement, and Skip for parsing and processing XML documents.

Vulnerability Detail

The encoding/xml package in golang before version 1.15.9 and 1.16.x before 1.16.1 is vulnerable to an infinite loop when a custom TokenReader returns EOF in the middle of an element. This vulnerability can be triggered during the decoding process using functions like Decode, DecodeElement, or Skip. An attacker can exploit this vulnerability by crafting a malicious XML document that triggers the infinite loop, leading to a denial-of-service (DoS) condition. This can potentially impact applications that rely on the encoding/xml package for XML parsing and processing.

Workaround

As a workaround, developers can implement additional checks in their code to validate the XML data before passing it to the encoding/xml package. This can include checking for unexpected EOF conditions or using alternative XML parsing libraries that are not affected by this vulnerability. Here is an example of how to validate XML data using the encoding/xml package in golang:

func validateXML(data []byte) error {
    // Check for unexpected EOF
    if len(data) == 0 {
        return errors.New("Empty XML data")
    }

    // Parse XML
    decoder := xml.NewDecoder(bytes.NewReader(data))
    for {
        _, err := decoder.Token()
        if err != nil {
            if err == io.EOF {
                break
            }
            return err
        }
    }

    return nil
}

Conclusion

In conclusion, the golang package is vulnerable to an infinite loop issue in the encoding/xml package. This can be exploited by an attacker to cause a denial-of-service condition in applications that rely on XML parsing and processing. To mitigate this vulnerability, it is crucial to update the golang package to the fixed versions (1.15.9 or 1.16.1) and recompile any affected applications. Additionally, implementing additional checks in the code to validate XML data can provide an extra layer of protection. For further assistance or support in vulnerability remediation, please contact DevNack.com.

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