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LES: Linux privilege escalation auditing tool

Quick download:

wget https://raw.githubusercontent.com/mzet-/linux-exploit-suggester/master/linux-exploit-suggester.sh -O les.sh

Details about LES usage and inner workings:

https://mzet-.github.io/2019/05/10/les-paper.html

Additional resources for the LES:

https://github.com/mzet-/les-res

Purpose

LES tool is designed to assist in detecting security deficiencies for a given Linux kernel/Linux-based machine. It provides following functionality:

Assessing kernel exposure on publicly known exploits

Tool assesses (using heuristics methods discussed in details here) exposure of the given kernel to publicly known Linux kernel exploits. Example of tool output:

$ ./linux-exploit-suggester.sh
...
[+] [CVE-2017-16995] eBPF_verifier

   Details: https://ricklarabee.blogspot.com/2018/07/ebpf-and-analysis-of-get-rekt-linux.html
   Exposure: highly probable
   Tags: debian=9.0{kernel:4.9.0-3-amd64},fedora=25|26|27,[ ubuntu=14.04 ]{kernel:4.4.0-89-generic},ubuntu=(16.04|17.04){kernel:4.(8|10).0-(19|28|45)-generic}
   Download URL: https://www.exploit-db.com/download/45010
   Comments: CONFIG_BPF_SYSCALL needs to be set && kernel.unprivileged_bpf_disabled != 1

[+] [CVE-2017-1000112] NETIF_F_UFO

   Details: http://www.openwall.com/lists/oss-security/2017/08/13/1
   Exposure: probable
   Tags: [ ubuntu=14.04{kernel:4.4.0-*} ],ubuntu=16.04{kernel:4.8.0-*}
   Download URL: https://raw.githubusercontent.com/xairy/kernel-exploits/master/CVE-2017-1000112/poc.c
   ext-url: https://raw.githubusercontent.com/bcoles/kernel-exploits/cve-2017-1000112/CVE-2017-1000112/poc.c
   Comments: CAP_NET_ADMIN cap or CONFIG_USER_NS=y needed. SMEP/KASLR bypass included. Modified version at 'ext-url' adds support for additional distros/kernels

[+] [CVE-2016-8655] chocobo_root

   Details: http://www.openwall.com/lists/oss-security/2016/12/06/1
   Exposure: probable
   Tags: [ ubuntu=(14.04|16.04){kernel:4.4.0-(21|22|24|28|31|34|36|38|42|43|45|47|51)-generic} ]
   Download URL: https://www.exploit-db.com/download/40871
   Comments: CAP_NET_RAW capability is needed OR CONFIG_USER_NS=y needs to be enabled
...

For each exploit, exposure is calculated. Following 'Exposure' states are possible:

  • Highly probable - assessed kernel is most probably affected and there's a very good chance that PoC exploit will work out of the box without any major modifications.

  • Probable - it's possible that exploit will work but most likely customization of PoC exploit will be needed to suit your target.

  • Less probable - additional manual analysis is needed to verify if kernel is affected.

  • Unprobable - highly unlikely that kernel is affected (exploit is not displayed in the tool's output)

Verifying state of kernel hardening security measures

LES can check for most of security settings available by your Linux kernel. It verifies not only the kernel compile-time configurations (CONFIGs) but also verifies run-time settings (sysctl) giving more complete picture of security posture for running kernel. This functionality is modern continuation of --kernel switch from checksec.sh tool by Tobias Klein. Example of tool output:

$ ./linux-exploit-suggester.sh --checksec

Mainline kernel protection mechanisms:

 [ Disabled ] GCC stack protector support (CONFIG_HAVE_STACKPROTECTOR)
              https://github.com/mzet-/les-res/blob/master/features/stackprotector-regular.md

 [ Disabled ] GCC stack protector STRONG support (CONFIG_STACKPROTECTOR_STRONG)
              https://github.com/mzet-/les-res/blob/master/features/stackprotector-strong.md

 [ Enabled  ] Low address space to protect from user allocation (CONFIG_DEFAULT_MMAP_MIN_ADDR)
              https://github.com/mzet-/les-res/blob/master/features/mmap_min_addr.md

 [ Disabled ] Restrict unprivileged access to kernel syslog (CONFIG_SECURITY_DMESG_RESTRICT)
              https://github.com/mzet-/les-res/blob/master/features/dmesg_restrict.md

 [ Enabled  ] Randomize the address of the kernel image (KASLR) (CONFIG_RANDOMIZE_BASE)
              https://github.com/mzet-/les-res/blob/master/features/kaslr.md

 [ Disabled ] Hardened user copy support (CONFIG_HARDENED_USERCOPY)
              https://github.com/mzet-/les-res/blob/master/features/hardened_usercopy.md

...

Usage

Assess exposure of the Linux box to publicly known exploits:

$ ./linux-exploit-suggester.sh

Show state of security features on the Linux box:

$ ./linux-exploit-suggester.sh --checksec

Assess exposure of Linux kernel on publicly known exploits based on the provided 'uname' string (i.e. output of uname -a command):

$ ./linux-exploit-suggester.sh --uname <uname-string>

For more usage examples, see here.

Getting involved

You hopefully now know what LES is and what it can do for you. Now see what you can do for LES:

  • Add newly published Linux privilege escalation exploits to it.
  • Test existing exploits on various Linux distributions with multiple kernel versions, then document your findings in a form of Tags in LES, e.g. of a tag: ubuntu=12.04{kernel:3.(2|5).0-(23|29)-generic} which states: tagged exploit was verifed to work correctly on Ubuntu 12.04 with kernels: 3.2.0-23-generic, 3.2.0-29-generic, 3.5.0-23-generic and 3.5.0-29-generic;. With this tag added LES will automatically highlight and bump dynamic Rank of the exploit when run on Ubuntu 12.04 with one of listed kernel versions. This will help you (and others) during pentests to rapidly identify critically vulnerable Linux machines.
  • Published exploits are often written only for PoC purposes only for one (or couple of) specific Linux distributions and/or kernel version(s). Pick sources of the exploit of choice and customize it to run on different kernel version(s). Then add your customized version of exploit as ext-url entry to LES and modify Tags to reflect newly added targets. See this article for an excellent example of adapting specific PoC exploit to different kernel versions.
  • Conduct source code analysis of chosen kernel hardening security measure then add it to the FEATURES array (if not already there) and publish your analysis at: https://github.com/mzet-/les-res/blob/master/features/<feature-name>.md.

Acknowledgments

bcoles for his excellent and frequent contributions to LES.