Java Remote Method Invocation, or Java RMI, ni mekanizma ya RPC iliyo na mwelekeo wa kitu inayoruhusu kitu kilichopo katika Java virtual machine moja kuita mbinu kwenye kitu kilichopo katika Java virtual machine nyingine. Hii inawawezesha waendelezaji kuandika programu zilizogawanywa kwa kutumia mtindo wa mwelekeo wa kitu. Utangulizi mfupi wa Java RMI kutoka mtazamo wa mashambulizi unaweza kupatikana katika hii hotuba ya blackhat.
PORT STATE SERVICE VERSION
1090/tcp open ssl/java-rmi Java RMI
9010/tcp open java-rmi Java RMI
37471/tcp open java-rmi Java RMI
40259/tcp open ssl/java-rmi Java RMI
Kawaida, ni sehemu za Java RMI za default (RMI Registry na Activation System) pekee ndizo zinazofungwa kwenye bandari za kawaida. Vitu vya mbali vinavyotekeleza programu halisi ya RMI kawaida vinafungwa kwenye bandari za nasibu kama inavyoonyeshwa kwenye matokeo hapo juu.
nmap mara nyingine huwa na shida kutambua huduma za RMI zilizolindwa na SSL. Ikiwa unakutana na huduma isiyojulikana ya ssl kwenye bandari ya kawaida ya RMI, unapaswa kuchunguza zaidi.
RMI Components
Kwa maneno rahisi, Java RMI inaruhusu mendelezi kufanya Java object ipatikane kwenye mtandao. Hii inafungua bandari ya TCP ambapo wateja wanaweza kuungana na kuita mbinu kwenye kitu kinacholingana. Ingawa hii inasikika rahisi, kuna changamoto kadhaa ambazo Java RMI inahitaji kutatua:
Ili kutuma wito wa mbinu kupitia Java RMI, wateja wanahitaji kujua anwani ya IP, bandari inayosikiliza, darasa au interface iliyotekelezwa na ObjID ya kitu kilichokusudiwa ( ObjID ni kitambulisho cha kipekee na nasibu ambacho kinaundwa wakati kitu kinapatikana kwenye mtandao. Inahitajika kwa sababu Java RMI inaruhusu vitu vingi kusikiliza kwenye bandari moja ya TCP).
Wateja wa mbali wanaweza kugawa rasilimali kwenye seva kwa kuita mbinu kwenye kitu kilichofichuliwa. Java virtual machine inahitaji kufuatilia ni zipi kati ya rasilimali hizi bado zinatumika na zipi kati yao zinaweza kukusanywa kama taka.
Changamoto ya kwanza inatatuliwa na RMI registry, ambayo kimsingi ni huduma ya upatanishi kwa Java RMI. RMI registry yenyewe pia ni RMI service, lakini interface iliyotekelezwa na ObjID ni thabiti na inajulikana na wateja wote wa RMI. Hii inaruhusu wateja wa RMI kutumia RMI registry kwa kujua tu bandari inayolingana ya TCP.
Wakati waendelezaji wanataka kufanya Java objects zao zipatikane ndani ya mtandao, kawaida huziunganisha na RMI registry. Registry inahifadhi taarifa zote zinazohitajika kuungana na kitu (anwani ya IP, bandari inayosikiliza, darasa au interface iliyotekelezwa na thamani ya ObjID) na inafanya ipatikane chini ya jina linaloweza kusomeka na binadamu (jina lililofungwa). Wateja wanaotaka kutumia RMI service wanauliza RMI registry kwa jina lililofungwa linalolingana na registry inarudisha taarifa zote zinazohitajika kuungana. Hivyo, hali ni sawa na huduma ya kawaida ya DNS. Orodha ifuatayo inaonyesha mfano mdogo:
importjava.rmi.registry.Registry;importjava.rmi.registry.LocateRegistry;importlab.example.rmi.interfaces.RemoteService;publicclassExampleClient {privatestaticfinalString remoteHost ="172.17.0.2";privatestaticfinalString boundName ="remote-service";publicstaticvoidmain(String[] args){try {Registry registry =LocateRegistry.getRegistry(remoteHost); // Connect to the RMI registryRemoteService ref = (RemoteService)registry.lookup(boundName); // Lookup the desired bound nameString response =ref.remoteMethod(); // Call a remote method} catch( Exception e) {e.printStackTrace();}}}
The second of the above mentioned challenges is solved by the Distributed Garbage Collector (DGC). This is another RMI service with a well known ObjID value and it is available on basically each RMI endpoint. When an RMI client starts to use an RMI service, it sends an information to the DGC that the corresponding remote object is in use. The DGC can then track the reference count and is able to cleanup unused objects.
Pamoja na Activation System iliyoshindikana, hizi ndizo sehemu tatu za kawaida za Java RMI:
The RMI Registry (ObjID = 0)
The Activation System (ObjID = 1)
The Distributed Garbage Collector (ObjID = 2)
The default components of Java RMI have been known attack vectors for quite some time and multiple vulnerabilities exist in outdated Java versions. From an attacker perspective, these default components are interisting, because they implemented known classes / interfaces and it is easily possible to interact with them. This situation is different for custom RMI services. To call a method on a remote object, you need to know the corresponding method signature in advance. Without knowing an existing method signature, there is no way to communicate to a RMI service.
RMI Enumeration
remote-method-guesser is a Java RMI vulnerability scanner that is capable of identifying common RMI vulnerabilities automatically. Whenever you identify an RMI endpoint, you should give it a try:
$ rmg enum 172.17.0.2 9010
[+] RMI registry bound names:
[+]
[+] - plain-server2
[+] --> de.qtc.rmg.server.interfaces.IPlainServer (unknown class)
[+] Endpoint: iinsecure.dev:37471 TLS: no ObjID: [55ff5a5d:17e0501b054:-7ff7, 3638117546492248534]
[+] - legacy-service
[+] --> de.qtc.rmg.server.legacy.LegacyServiceImpl_Stub (unknown class)
[+] Endpoint: iinsecure.dev:37471 TLS: no ObjID: [55ff5a5d:17e0501b054:-7ffc, 708796783031663206]
[+] - plain-server
[+] --> de.qtc.rmg.server.interfaces.IPlainServer (unknown class)
[+] Endpoint: iinsecure.dev:37471 TLS: no ObjID: [55ff5a5d:17e0501b054:-7ff8, -4004948013687638236]
[+]
[+] RMI server codebase enumeration:
[+]
[+] - http://iinsecure.dev/well-hidden-development-folder/
[+] --> de.qtc.rmg.server.legacy.LegacyServiceImpl_Stub
[+] --> de.qtc.rmg.server.interfaces.IPlainServer
[+]
[+] RMI server String unmarshalling enumeration:
[+]
[+] - Caught ClassNotFoundException during lookup call.
[+] --> The type java.lang.String is unmarshalled via readObject().
[+] Configuration Status: Outdated
[+]
[+] RMI server useCodebaseOnly enumeration:
[+]
[+] - Caught MalformedURLException during lookup call.
[+] --> The server attempted to parse the provided codebase (useCodebaseOnly=false).
[+] Configuration Status: Non Default
[+]
[+] RMI registry localhost bypass enumeration (CVE-2019-2684):
[+]
[+] - Caught NotBoundException during unbind call (unbind was accepeted).
[+] Vulnerability Status: Vulnerable
[+]
[+] RMI Security Manager enumeration:
[+]
[+] - Security Manager rejected access to the class loader.
[+] --> The server does use a Security Manager.
[+] Configuration Status: Current Default
[+]
[+] RMI server JEP290 enumeration:
[+]
[+] - DGC rejected deserialization of java.util.HashMap (JEP290 is installed).
[+] Vulnerability Status: Non Vulnerable
[+]
[+] RMI registry JEP290 bypass enmeration:
[+]
[+] - Caught IllegalArgumentException after sending An Trinh gadget.
[+] Vulnerability Status: Vulnerable
[+]
[+] RMI ActivationSystem enumeration:
[+]
[+] - Caught IllegalArgumentException during activate call (activator is present).
[+] --> Deserialization allowed - Vulnerability Status: Vulnerable
[+] --> Client codebase enabled - Configuration Status: Non Default
Matokeo ya hatua ya kuorodhesha yanaelezewa kwa undani zaidi katika kurasa za hati za mradi. Kulingana na matokeo, unapaswa kujaribu kuthibitisha udhaifu ulioainishwa.
Thamani za ObjID zinazonyeshwa na remote-method-guesser zinaweza kutumika kubaini muda wa huduma. Hii inaweza kuruhusu kubaini udhaifu mwingine:
Hata wakati hakuna udhaifu ulioainishwa wakati wa kuhesabu, huduma za RMI zilizopo zinaweza bado kufichua kazi hatari. Zaidi ya hayo, licha ya mawasiliano ya RMI na vipengele vya kawaida vya RMI kulindwa na filters za deserialization, wakati wa kuzungumza na huduma za RMI za kawaida, filters kama hizo kwa kawaida hazipo. Kujua saini sahihi za mbinu kwenye huduma za RMI ni muhimu.
Kwa bahati mbaya, Java RMI haisaidii kuhesabu mbinu kwenye objects za mbali. Hata hivyo, inawezekana kufanyia kazi saini za mbinu kwa kutumia zana kama remote-method-guesser au rmiscout:
Mbali na kukisia, unapaswa pia kutafuta katika injini za utafutaji au GitHub kwa ajili ya interface au hata utekelezaji wa huduma ya RMI uliokutana nayo. Jina la bound na jina la darasa au interface iliyotekelezwa linaweza kuwa na msaada hapa.
Known Interfaces
remote-method-guesser inaashiria madarasa au interfaces kama known ikiwa yanatajwa katika hifadhidata ya ndani ya zana ya huduma za RMI zinazojulikana. Katika kesi hizi unaweza kutumia hatua ya known kupata maelezo zaidi kuhusu huduma husika ya RMI:
$ rmg enum 172.17.0.2 1090 | head -n 5
[+] RMI registry bound names:
[+]
[+] - jmxrmi
[+] --> javax.management.remote.rmi.RMIServerImpl_Stub (known class: JMX Server)
[+] Endpoint: localhost:41695 TLS: no ObjID: [7e384a4f:17e0546f16f:-7ffe, -553451807350957585]
$ rmg known javax.management.remote.rmi.RMIServerImpl_Stub
[+] Name:
[+] JMX Server
[+]
[+] Class Name:
[+] - javax.management.remote.rmi.RMIServerImpl_Stub
[+] - javax.management.remote.rmi.RMIServer
[+]
[+] Description:
[+] Java Management Extensions (JMX) can be used to monitor and manage a running Java virtual machine.
[+] This remote object is the entrypoint for initiating a JMX connection. Clients call the newClient
[+] method usually passing a HashMap that contains connection options (e.g. credentials). The return
[+] value (RMIConnection object) is another remote object that is when used to perform JMX related
[+] actions. JMX uses the randomly assigned ObjID of the RMIConnection object as a session id.
[+]
[+] Remote Methods:
[+] - String getVersion()
[+] - javax.management.remote.rmi.RMIConnection newClient(Object params)
[+]
[+] References:
[+] - https://docs.oracle.com/javase/8/docs/technotes/guides/management/agent.html
[+] - https://github.com/openjdk/jdk/tree/master/src/java.management.rmi/share/classes/javax/management/remote/rmi
[+]
[+] Vulnerabilities:
[+]
[+] -----------------------------------
[+] Name:
[+] MLet
[+]
[+] Description:
[+] MLet is the name of an MBean that is usually available on JMX servers. It can be used to load
[+] other MBeans dynamically from user specified codebase locations (URLs). Access to the MLet MBean
[+] is therefore most of the time equivalent to remote code execution.
[+]
[+] References:
[+] - https://github.com/qtc-de/beanshooter
[+]
[+] -----------------------------------
[+] Name:
[+] Deserialization
[+]
[+] Description:
[+] Before CVE-2016-3427 got resolved, JMX accepted arbitrary objects during a call to the newClient
[+] method, resulting in insecure deserialization of untrusted objects. Despite being fixed, the
[+] actual JMX communication using the RMIConnection object is not filtered. Therefore, if you can
[+] establish a working JMX connection, you can also perform deserialization attacks.
[+]
[+] References:
[+] - https://github.com/qtc-de/beanshooter
Protocol_Name: Java RMI #Protocol Abbreviation if there is one.
Port_Number: 1090,1098,1099,1199,4443-4446,8999-9010,9999 #Comma separated if there is more than one.
Protocol_Description: Java Remote Method Invocation #Protocol Abbreviation Spelled out
Entry_1:
Name: Enumeration
Description: Perform basic enumeration of an RMI service
Command: rmg enum {IP} {PORT}
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