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

• Maven org.http4k:http4k-format-xml: < 6.50.0.0 → fixed in 6.50.0.0

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 = """ Root element is: $rootElementName """.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: ``` org.jetbrains.kotlin kotlin-test-junit5 1.9.0 test org.junit.jupiter junit-jupiter-engine 5.10.0 test org.jetbrains.kotlin kotlin-stdlib 1.9.0 org.http4k http4k-core 5.40.0.0 org.http4k http4k-format-xml 5.40.0.0 org.http4k http4k-server-netty 5.40.0.0 ``` Exploit payload example to trigger SSRF `curl -X POST http://localhost:9000 -H "Content-Type: application/xml" -d "]>&xxe;"` 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 Follow-up patch — v6.50.0.0 (May 2026) The original fix shipped in v5.41.0.0 / v4.50.0.0 closed the documented external-entity attack class (SSRF, local-file disclosure, code execution) by setting `ACCESS_EXTERNAL_DTD=""`, `ACCESS_EXTERNAL_SCHEMA=""`, and `isExpandEntityReferences=false` on the default `DocumentBuilderFactory`. A residual gap remained: the parser still accepted documents containing `` declarations even though external entity resolution was blocked. This left open billion-laughs-style internal entity expansion DoS attacks against any application using `Body.xml()` or `Document.asXmlDocument()` on untrusted XML. v6.50.0.0 closes this residual by adding `disallow-doctype-decl=true` and `FEATURE_SECURE_PROCESSING=true` to `defaultXmlParsingConfig`. Any document containing a `` is now rejected at parse time. Follow-up affected & fixed versions | Version | Fixed Version | |---------|---------------| | `>= 5.41.0.0, ` rejection and billion-laughs payload rejection | | 31/05/2026 18:06 | http4k v6.50.0.0 released to Maven Central |