awesome-linux-rootkits/details/reptile.md

Reptile kernel rootkit details

https://github.com/f0rb1dd3n/Reptile

• not able to tamper file contents while reading byte-by-byte (❗)
• not able to hide all threads and children of hidden (parent) process (❗)

Environment

• x86, x86_64
• Linux kernel 2.6.x/3.x/4.x

Persistency

Boot-time module loading using OS-specific startup files:

• /etc/modules (debian/ubuntu)
• /etc/rc.modules (redhat/centos/fedora)

https://github.com/linux-rootkits/Reptile/blob/master/setup.sh#L296

Detection evasion

Rootkit is trying to evade from detection by:

• hiding files by name
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L575
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L619
• tampering contents of startup files while reading
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L638
• hiding kernel module by unlinking from modules-list
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L145
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L157

Management interface

Implemented via kill(2) by hooking sys_call_table[__NR_kill] entry:

• https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L509

Supported commands are:

• hiding/unhiding processes
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L518
• hiding/unhiding rootkit's module
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L514
• enabling/disabling of tampering file content function
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L524
• gaining root priveleges to calling process
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L528

Altering system behaviour

Hooking of system calls by patching syscall-handlers in sys_call_table[]:

• to write to read-only page CR0/WP technique used (x86-only)
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L681
• netfilter hook (NF_IP_PRI_FIRST)
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L356
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L687

Hiding (tampering) of file contents

Filtering of file content while reading:

• hook sys_call_table[__NR_read]
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L638

Hiding of files and directories

Filtering of directory entries:

• hook sys_call_table[__NR_getdents]
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L594
• hook sys_call_table[__NR_getdents64]
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L550

Hiding of processes and process trees

Filtering PID-like numeric entries while listing /proc:

• getdents/getdents64 hook used
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L619
• hidden tasks are marked using task->flags (bit 0x10000000)
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L189

Backdoor/shell

Reverse shell spawning by port-knocking-like technique:

• magic packet with token used (ICMP/UDP/TCP)
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L356
• spawning root-shell connection to remote host
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L328
  • https://github.com/linux-rootkits/Reptile/blob/master/rep_mod.c#L210