Linux privilege escalation: kernel exploits

Before executing it by your low-priv user make sure to set the suid-bit on it, like this:.And you should connect without requiring a password.The ability to execute the exploit on the target.Additional permissions that are not required or necessary can lead to misuse of these permissions, which is why privilege escalation plays a significant role in detecting any malicious activity.Always patch your systems! Subscribe to our newsletter.Privilege Escalation through sudo – Linux.Hello guys, in our last blog of the series we discussed basic fundamentals about Android applications and their architecture, if you have not read my previous blog on Understanding Android Basics, the If you have access to an account with sudo-rights but you don’t have its password you can install a keylogger to get it.It usually occurs when a system has a bug that allows security to be bypassed or, alternatively, has flawed design assumptions about how it will be used.Open with Desktop View raw View blame.If the suid-bit is set on a program that can spawn a shell or in another way be abuse we could use that to escalate our Linux privilege escalation: kernel exploits.
Linux Kernel < - 'Netfilter Local Privilege Escalation - Linux local Exploit

Privilege Escalation – Though I would not suggest to completely rely on this database while searching for Linux Kernel exploits.We added code to set effective capabilities required to reach vulnerable code.Seccomp is great in limiting unnecessary kernel entry points.Test if you can create files, then check with your low-priv shell what user has created that file.It is not a cheat sheet for enumeration using Linux commands.

There are often Metasploit modules available that will allow to escalate privileges by exploiting known kernel exploit.Although Kernel Exploits are often an easy way to root, they should be the last resort when conducting a penetration test, as some of them have a risk of breaking the machine and a fair number of them will only run once.

Save my name, email, and website in this browser for the next time I comment.Through this blog, I would like to share my passion for penetration testing, hoping that this might be of help for other students and professionals out there.I will be more than glad to exchange ideas with other fellow pentesters and enthusiasts.

Guides , Linux , Privilege Escalation.January 22, by Stefano Lanaro Leave a comment.Introduction The kernel is a component of the operating system that sits at the core of it, it has complete control over everything that occurs in the system.Automated enumeration Automated enumeration scripts such as LinPEAS can be used to enumerate operating system and kernel information as well: Finding Available Kernel Exploits The next step is to find out whether there are any known exploits available that affect the kernel version used by the machine.

Manual Enumeration SearchSploit can be used to find kernel exploits, the syntax is as follows: searchsploit linux kernel x.Additionally, the Exploit Suggester Metasploit module can be used to carry out this task, by selecting the module, setting the session and running it: Compiling the Exploit If the machine has GCC or other installed, Kernel exploits should always be compiled on the target machine, as it is more likely to run without issues.

The following command can be used to compile exploits with GCC: gcc exploit.Manual Exploitation Once the exploit has been transferred to the victim machine, using tools such as wget or curl, its permissions have to be changed to make it executable.

These can be used by selecting the exploit and setting the options: session to specify the meterpreter session to run the exploit against payload to specify the payload type, in this case the Linux reverse TCP shell LHOST to specify the local host IP address to connect to LPORT to specify the local port to connect to In this case, the Metasploit counterpart of the same exploit did not work.

Conclusion Although Kernel Exploits are often an easy way to root, they should be the last resort when conducting a penetration test, as some of them have a risk of breaking the machine and a fair number of them will only run once.Previous post.Next post.This blog is particularly aimed at helping beginners understand the fundamentals of Linux privilege escalation with examples.It is not a cheat sheet for enumeration using Linux commands.Privilege escalation is all about proper enumeration.

There are multiple ways to perform the same tasks that I have shown in the examples.Linux has inherited from UNIX the concept of ownerships and permissions for files.

File permissions are one way the system protects itself from malicious tampering.On a UNIX web server, every single file and folder stored on the hard drive has a set of permissions associated with it, which says who is allowed to do what with the file.If any other user tries to read this file, he cannot read it.

We can see the permission denied error, when I tried reading the file when I am not a superuser.We will not go into permission model details here as it is another big topic.

However, the superuser root can access all the files which are present on the system.In order to change any important configuration or perform any further attack, first we need to get root access on any Linux based system.

We assume that now we have shell on the remote system.Kernel exploits are programs that leverage kernel vulnerabilities in order to execute arbitrary code with elevated permissions.Successful kernel exploits typically give attackers super user access to target systems in the form of a root command prompt.

In many cases, escalating to root on a Linux system is as simple as downloading a kernel exploit to the target file system, compiling the exploit, and then executing it.Assuming that we can run code as an unprivileged user, this is the generic workflow of a kernel exploit.Trick the kernel into running our payload in kernel mode 2.Manipulate kernel data, e.Launch a shell with new privileges Get root! A vulnerable kernel 2.A matching exploit 3.

The ability to transfer the exploit onto the target 4.The ability to execute the exploit on the target.The easiest way to defend against kernel exploits is to keep the kernel patched and updated.

In the absence of patches, administrators can strongly influence the ability to transfer and execute the exploit on the target.When these programs are required, their use should be limited to specific users, directories, applications such as SCP , and specific IP addresses or domains.

An unprivileged local user could use this flaw to gain write access to otherwise read-only memory mappings and thus increase their privileges on the system.It was one of the most serious privilege escalation vulnerability ever discovered and it affected almost all the major Linux distros.Exploiting a vulnerable machine via dirtycow.There are a lot of different local privilege escalation exploits publicly available for different Kernel and OS.Whether you can get root access on a Linux host using a kernel exploit depends upon whether the kernel is vulnerable or not.

Kali Linux has a local copy of exploit-db exploits which make it easier to search for local root exploits.Though I would not suggest to completely rely on this database while searching for Linux Kernel exploits.Though, it feels very tempting to just run an exploit and get root access, but you should always keep this as your last option.

The remote host might crash as many of the root exploits publicly available are not very stable.You might get root and then crash the box.You should always try the other techniques to get root which have been discussed below before directly jumping to run a local root exploit.The famous EternalBlue and SambaCry exploit, exploited smb service which generally runs as root.

With just one exploit, an attacker can get remote code execution and Local Privilege Escalation as well.You should always check if web servers, mail servers, database servers, etc.

Many a times, web admins run these services as root and forget about the security issues it might cause.There could be services which run locally and are not exposed publicly which can also be exploited.We can check for services which are running locally if they could be exploited or not.Exploiting a vulnerable version of MySQL which is running as root to get root access.If mysql is running with root privileges, the commands will be executed as root.

One of the biggest mistake web admins do, is to run a webserver with root privilege.A command injection vulnerability on the web application can lead an attacker to root shell.

This is a classic example of why you should never run any service as root unless really required.Binary exploits of a root owned program are far less dangerous than a kernel exploit because even if the service crashes, the host machine will not crash and the services will probably auto restart.

SUID which stands for set user ID, is a Linux feature that allows users to execute a file with the permissions of a specified user.For example, the Linux ping command typically requires root permissions in order to open raw network sockets.By marking the ping program as SUID with the owner as root, ping executes with root privileges anytime a low privilege user executes the program.SUID is a feature that, when used properly, actually enhances Linux security.

The problem is that administrators may unknowingly introduce dangerous SUID configurations when they install third party applications or make logical configuration changes.SUID bit should not be set especially on any file editor as an attacker can overwrite any files present on the system.Exploiting vulnerable SUID executable to get root access.Once he has access to any of the SUDO users, he can basically execute any commands with root privileges.

Administrators might just allow the users to run a few commands through SUDO and not all of them but even with this configuration, they might introduce vulnerabilities unknowingly which can lead to privilege escalation.Exploiting misconfigured SUDO rights to get root access.We can run find, cat and python as SUDO.These all commands will run as root when run with SUDO.

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Weak/reused/plaintext passwords.Inside service.Suid misconfiguration.

How to use:

  1. Because of this, exploiting vulnerabilities in the kernel will pretty much always result in a full system compromise.
  2. Has the user installed some third party software that might be vulnerable?
  3. The exploit, however, performs identically with one major difference in the final result.
  4. Privilege escalation is the act of exploiting a bug, design flaw or configuration oversight in an operating system or software application to gain elevated access to resources that are normally protected by an application or user.
  5. Seccomp is great in limiting unnecessary kernel entry points.
Linux Privilege Escalation – Kernel Exploits, time: 3:40

Linux Kernel Privilege Escalation Vulnerability (CVE-2020-14386) Threat Alert

We are re-running the very same exploit, and break the kernel just before it executes the vulnerable path.Alternatively you can use the following lines to add a dummy user without a password.

Linux Privilege Escalation – Kernel Exploits – properties

  • Which contains user space utilities for Linux CAN subsystem.
  • Precompiled exploits can be found inside these repositories, run them at your own risk!
  • When the sun sets, I put on my hoodie, fire up Linux VMs and debuggers to look under the hood of technologies that make up the cloud native ecosystem.
  • Which contains user space utilities for Linux CAN subsystem.
  • Binary exploits of a root owned program are far less dangerous than a kernel exploit because even if the service crashes, the host machine will not crash and the services will probably auto restart.
  • The problem is that administrators may unknowingly introduce dangerous SUID configurations when they install third party applications or make logical configuration changes.
  • In this case, we are using an mlock system call, which we can manually trigger from the exploit whenever we want to look at the internal state of the running process.
  • If stuck, the – vvv verbosity should provide enough details as to why.

What is Privilege escalation?

: For more of these and how to use the see the next section about abusing sudo-rights:.

What we usually need to know to test if a kernel exploit works is the OS, architecture and kernel version.The famous EternalBlue and SambaCry exploit, exploited smb service which generally runs as root.

  • Binary exploits of a root owned program are far less dangerous than a kernel exploit because even if the service crashes, the host machine will not crash and the services will probably auto restart.
  • Don’t use kernel exploits if you can avoid it.
  • They can also produce a lot of stuff in the sys.
  • All of these actions require some sort of process to happen in the kernel space.
  • If any other user tries to read this file, he cannot read it.

Linux has inherited from UNIX the concept of ownerships and permissions for files.File permissions are one way the system protects itself from malicious tampering.On a UNIX web server, every single file and folder stored on the hard drive has a set of permissions associated with it, which says who is allowed to do what with the file.If any other user tries to read this file, he cannot read it.

We can see the permission denied error, when I tried reading the file when I am not a superuser.We will not go into permission model details here as it is another big topic.However, the superuser root can access all the files which are present on the system.In order to change any important configuration or perform any further attack, first we need to get root access on any Linux based system.

We assume that now we have shell on the remote system.Kernel exploits are programs that leverage kernel vulnerabilities in order to execute arbitrary code with elevated permissions.

Successful kernel exploits typically give attackers super user access to target systems in the form of a root command prompt.In many cases, escalating to root on a Linux system is as simple as downloading a kernel exploit to the target file system, compiling the exploit, and then executing it.

Assuming that we can run code as an unprivileged user, this is the generic workflow of a kernel exploit.Trick the kernel into running our payload in kernel mode 2.Manipulate kernel data, e.Launch a shell with new privileges Get root!

A vulnerable kernel 2.A matching exploit 3.The ability to transfer the exploit onto the target 4.The ability to execute the exploit on the target.The easiest way to defend against kernel exploits is to keep the kernel patched and updated.In the absence of patches, administrators can strongly influence the ability to transfer and execute the exploit on the target.When these programs are required, their use should be limited to specific users, directories, applications such as SCP , and specific IP addresses or domains.

An unprivileged local user could use this flaw to gain write access to otherwise read-only memory mappings and thus increase their privileges on the system.

It was one of the most serious privilege escalation vulnerability ever discovered and it affected almost all the major Linux distros.Exploiting a vulnerable machine via dirtycow.There are a lot of different local privilege escalation exploits publicly available for different Kernel and OS.Whether you can get root access on a Linux host using a kernel exploit depends upon whether the kernel is vulnerable or not.Kali Linux has a local copy of exploit-db exploits which make it easier to search for local root exploits.

Though I would not suggest to completely rely on this database while searching for Linux Kernel exploits.Though, it feels very tempting to just run an exploit and get root access, but you should always keep this as your last option.The remote host might crash as many of the root exploits publicly available are not very stable.You might get root and then crash the box.You should always try the other techniques to get root which have been discussed below before directly jumping to run a local root exploit.

The famous EternalBlue and SambaCry exploit, exploited smb service which generally runs as root.With just one exploit, an attacker can get remote code execution and Local Privilege Escalation as well.

You should always check if web servers, mail servers, database servers, etc.Many a times, web admins run these services as root and forget about the security issues it might cause.There could be services which run locally and are not exposed publicly which can also be exploited.We can check for services which are running locally if they could be exploited or not.

Exploiting a vulnerable version of MySQL which is running as root to get root access.If mysql is running with root privileges, the commands will be executed as root.One of the biggest mistake web admins do, is to run a webserver with root privilege.A command injection vulnerability on the web application can lead an attacker to root shell.This is a classic example of why you should never run any service as root unless really required.

Binary exploits of a root owned program are far less dangerous than a kernel exploit because even if the service crashes, the host machine will not crash and the services will probably auto restart.SUID which stands for set user ID, is a Linux feature that allows users to execute a file with the permissions of a specified user.

For example, the Linux ping command typically requires root permissions in order to open raw network sockets.By marking the ping program as SUID with the owner as root, ping executes with root privileges anytime a low privilege user executes the program.SUID is a feature that, when used properly, actually enhances Linux security.The problem is that administrators may unknowingly introduce dangerous SUID configurations when they install third party applications or make logical configuration changes.

SUID bit should not be set especially on any file editor as an attacker can overwrite any files present on the system.Exploiting vulnerable SUID executable to get root access.Once he has access to any of the SUDO users, he can basically execute any commands with root privileges.Administrators might just allow the users to run a few commands through SUDO and not all of them but even with this configuration, they might introduce vulnerabilities unknowingly which can lead to privilege escalation.

Exploiting misconfigured SUDO rights to get root access.We can run find, cat and python as SUDO.These all commands will run as root when run with SUDO.If we can somehow escape to the shell through any of these commands, we can get root access.Cron jobs, if not configured properly can be exploited to get root privilege.Any script or binaries in cron jobs which are writable?

Can we write over the cron file itself.So test them all out and see which one you like best.By exploiting vulnerabilities in the Linux Kernel we can sometimes escalate our privileges.

What we usually need to know to test if a kernel exploit works is the OS, architecture and kernel version.Don’t use kernel exploits if you can avoid it.If you use it it might crash the machine or put it in an unstable state.So kernel exploits should be the last resort.Always use a simpler priv-esc if you can.They can also produce a lot of stuff in the sys.

So if you find anything good, put it up on your list and keep searching for other ways before exploiting it.The idea here is that if specific service is running as root and you can make that service execute commands you can execute commands as root.

Look for webserver, database or anything else like that.A typical example of this is mysql, example is below.If you find that mysql is running as root and you username and password to log in to the database you can issue the following commands:.Has the user installed some third party software that might be vulnerable?

Check it out.If you find anything google it for exploits.It might be that case that the user is running some service that is only available from that host.You can’t connect to the service from the outside.It might be a development server, a database, or anything else.

These services might be running as root, or they might have vulnerabilities in them.They might be even more vulnerable since the developer or user might be thinking “since it is only accessible for the specific user we don’t need to spend that much of security”.Check the netstat and compare it with the nmap-scan you did from the outside.

Do you find more services available from the inside? When a binary with suid permission is run it is run as another user, and therefore with the other users privileges.It could be root, or just another user.If the suid-bit is set on a program that can spawn a shell or in another way be abuse we could use that to escalate our privileges.If these programs have suid-bit set we can use them to escalate privileges too.

For more of these and how to use the see the next section about abusing sudo-rights:.If you have a limited shell that has access to some programs using sudo you might be able to escalate your privileges with.Any program that can write or overwrite can be used.If you find a script that is owned by root but is writable by anyone you can add your own malicious code in that script that will escalate your privileges when the script is run as root.

Under Attack

Kernel exploit in a container.Browse Resources.

CVE-2019-13272 Exploit PoC – Linux Kernel 4.10 – 5.1.17 Exploit – Privilege Escalation, time: 2:43
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