CVE-2023-29400: Improper handling of empty HTML attributes in html/template

Background

The stdlib package in the Go ecosystem provides a set of standard libraries for the Go programming language. One of the packages within stdlib is html/template, which is used for generating HTML output. The html/template package allows developers to define templates with placeholders that can be filled with dynamic data. These templates can contain actions in unquoted HTML attributes, such as "attr={{.}}". However, when these templates are executed with empty input, the output may have unexpected results due to HTML normalization rules. This can potentially lead to the injection of arbitrary attributes into HTML tags.

Vulnerability Detail

The vulnerability arises from the improper handling of empty HTML attributes in the html/template package. When a template with actions in unquoted HTML attributes is executed with empty input, the resulting output may be parsed incorrectly due to HTML normalization rules. This can be exploited by an attacker to inject arbitrary attributes into HTML tags, potentially leading to cross-site scripting (XSS) attacks or other security vulnerabilities.

go get stdlib@vgo1.25.5

Workaround

If upgrading to the fixed version is not immediately feasible, developers can implement a workaround by manually sanitizing and validating the input data before executing the template. This involves ensuring that the input data for the template does not contain any malicious or unexpected content. Here's an example of how to sanitize the input data using the html/template package:

import (
    "html/template"
    "net/http"
)

func handler(w http.ResponseWriter, r *http.Request) {
    // Sanitize and validate the input data
    input := sanitizeInput(r.FormValue("input"))

    // Create a new template
    tmpl := template.New("mytemplate")

    // Parse the template
    tmpl, err := tmpl.Parse("<div attr={{.}}></div>")
    if err != nil {
        // Handle error
        return
    }

    // Execute the template with the sanitized input
    err = tmpl.Execute(w, input)
    if err != nil {
        // Handle error
        return
    }
}

Conclusion

In conclusion, the stdlib package in the Go ecosystem is vulnerable to improper handling of empty HTML attributes in the html/template package. This can result in the injection of arbitrary attributes into HTML tags, potentially leading to security vulnerabilities. To fix this issue, developers should upgrade to version 1.19.9 or later of the stdlib package. If immediate upgrading is not possible, a workaround can be implemented by sanitizing and validating the input data before executing the template. For further support on vulnerability remediation, please contact DevNack.com.

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