A security vulnerability (CVE-2023-39319) has been discovered in the html/template package, which may lead to Cross-Site Scripting (XSS) attacks if exploited. This vulnerability affects the handling of " contexts. As a result, the template parser might not properly apply rules to terminate script contexts and subsequently fail in escaping actions, making the system prone to XSS attacks.

In this post, we delve into the details of the CVE-2023-39319 vulnerability, provide code snippets demonstrating the issue, and discuss potential exploits. This information could be crucial in formulating a timely and efficient response to safeguard your systems from potential attacks.

Problem Description

The html/template package is widely used for HTML generation and rendering in web applications, which necessitates the proper handling of various contexts like " contexts, the template parser does not apply the correct rules, causing actions to be improperly escaped.

For instance, the following code snippet

func main() {
    tmpl := template.Must(template.New("test").Parse(`
        <html>
        <body>
        <script>
        var x = "{{.}}";
        </script>
        </body>
        </html>`))

    _ = tmpl.Execute(os.Stdout, "</script><script>alert('XSS')</script>")
}

Would generate output such as

<html>
<body>
<script>
var x = "</script><script>alert('XSS')</script>";
</script>
<body>
</html>

As seen above, the html/template package did not properly escape the "

Exploit Details

The improper handling of "
- Injecting malicious JavaScript code via untrusted user inputs, potentially enabling attackers to steal sensitive information, hijack sessions, or deface websites.

- Crafting malicious URLs containing malicious script payloads that execute when unsuspecting users click on them or directly input them in their browsers.

- Manipulating cookies through JS code injection, posing a risk to user sessions and potentially leading the attacker to escalate privileges within the application.

Official Advisory: [LINK_TO_ADVISORY]

- CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-39319
- NIST National Vulnerability Database: https://nvd.nist.gov/vuln/detail/CVE-2023-39319

To mitigate the impact of this vulnerability, it is essential to

- Update the html/template package to a version that contains a fix for CVE-2023-39319, as soon as it becomes available.

Implement robust Content Security Policy (CSP) rules to minimize the risk of XSS exploitation.

- Regularly monitor system logs, user activity, and support channels for any signs of active exploitation or other suspicious activities.

Conclusion

CVE-2023-39319 poses a significant risk to web applications employing the html/template package due to improper handling of " contexts. Swift action to implement mitigation measures and install available security patches can minimize the risk of exploitation and help ensure the security of your systems.

Timeline

Published on: 09/08/2023 17:15:27 UTC
Last modified on: 11/25/2023 11:15:17 UTC