Linode Safety Digest Jan 30 – Feb 6 2022 | Linux Kernel eBPF

Date:


This week, we’ll talk about three excessive severity vulnerabilities that would enable attackers to escalate privileges if they’ve native entry to the system.

Linux Kernel eBPF – Improper Enter Validation Vulnerability

CVE-2022-23222 describes a vulnerability stemming from the kernel’s dealing with of eBPF applications. An attacker who can execute BPF might crash the system or execute arbitrary code within the context of the kernel.

Root Trigger – The BPF verifier doesn’t correctly limit a number of *_OR_NULL pointer sorts, which permits these sorts to do pointer arithmetic. This may be leveraged to execute arbitrary code or crash the system. 

Necessary notice: Unprivileged BPF will get disabled by default in most distros. The bug was launched in kernel model 5.8.0 and patched on kernel model 5.14.17. Availability of public exploits is one more reason why CVE-2022-23222 poses a big threat.

Holding updated with the newest kernel supplied by your Linux distribution is a simple option to shield your self from this vulnerability. In case your Linode boots a kernel offered by us, you’ll be able to confirm that your Linode’s Configuration Profile is about besides the most recent kernel after which reboot your Linode. 

If you happen to can not replace to a patched kernel instantly, you may as well mitigate this vulnerability by guaranteeing that  unprivileged_bpf_disabled is about to 1. The next instance will apply short-term mitigation till your Linode reboots. Be certain to jot down this setting to a sysctl configuration file and securely boot your Linode to persist the mitigation.

# sysctl -w kernel.unprivileged_bpf_disabled=1

Supply: Tr3e wang of SecCoder Safety Lab

Container Escape Utilizing Heap Overflow in Linux Kernel

CVE-2022-0185 is a heap overflow bug that enables an attacker with entry to an unprivileged consumer to escalate their privileges to root. To do that, the attacker will need to have a selected Linux functionality, CAP_SYS_ADMIN. You will need to notice that when Docker (or different CRIs) are utilized in a Kubernetes cluster, the seccomp filter will get disabled by default, so this vulnerability may very well be exploited in these circumstances.

Root Trigger – The bug is brought on by an integer underflow current in fs/fs_context.c:legacy_parse_param, leading to a sound max size miscalculation. This results in an integer underflow within the “File System Context” element. 

Underflow happens when a subtraction operation reduces an unsigned integer to a price beneath zero. Since unsigned integers can not signify destructive numbers, the ensuing calculation wraps across the integer’s max worth as a substitute. When this underflow happens throughout the legacy_parse_param operate, , a dimension verify fails, and the attacker can write past the bounds of the allotted 4kb reminiscence within the kernel house. Utilizing this “unbound write,” the attacker can change values within the kernel reminiscence and, for instance, add entry to themself to every other course of operating on the identical node.

The command “capsh –print” can be utilized within the context of the present consumer to record enabled capabilities. Exploitation depends on the CAP_SYS_ADMIN functionality; nonetheless, the permission solely must be granted within the present namespace. An unprivileged consumer can use unshare (CLONE_NEWNS | CLONE_NEWUSER) to enter a namespace with the CAP_SYS_ADMIN permission after which proceed with exploitation to root the system. Nevertheless, utilizing seccomp will stop the attacker from getting into the namespace with that functionality.

The vulnerability was launched in kernel 5.1 and patched in 5.16.2. The exploit code is already surfacing on-line. Right here is the unique write-up for extra technical particulars on the findings. 

Holding updated with the most recent kernel supplied by your Linux distribution is a simple option to shield your self from this vulnerability. In case your Linode boots a kernel offered by us, you may as well confirm that your Linode’s Configuration Profile is about besides the most recent kernel after which reboot your Linode. If you’re not capable of replace to a patched kernel instantly, you’ll be able to apply these mitigations:

  • Reduce the utilization of privileged containers which have entry to the CAP_SYS_ADMIN functionality. 
  • For unprivileged containers, be certain that a seccomp filter is in place that blocks the unshare name will cut back the danger.
  • Mitigate exploitation from unprivileged containers by disabling the consumer’s capability to make use of consumer namespaces at a number degree. The next instance will apply short-term mitigation till your Linode reboots. Be certain to jot down this setting to a sysctl configuration file and securely boot your Linode to persist the mitigation.
# sysctl -w kernel.unprivileged_userns_clone=0

PwnKit –  Native Privilege Escalation Vulnerability in Polkit

Polkit is a element for controlling system-wide privileges in Unix-like OSs. It offers a scientific methodology for non-privileged processes to speak with privileged processes. Moreover, somebody also can use polkit to execute instructions with elevated privileges utilizing the command pkexec (often with root). 

CVE-2021-4034 is a reminiscence corruption vulnerability in polkit’s pkexec, a SUID-root program put in by default on most main Linux distributions. Profitable exploitation permits any unprivileged consumer to achieve root privileges within the default configuration simply.

Root Trigger – The pkexec program doesn’t correctly validate the variety of arguments handed to it,  permitting somebody to execute arbitrary code as a privileged consumer. 

All Polkit variations from 2009 on are weak and exploitable even when the polkit daemon itself isn’t operating.

Holding updated with the most recent kernel supplied by your Linux distribution is a simple option to shield your self from this vulnerability. In case your Linode boots a kernel offered by us, you’ll be able to confirm that your Linode’s Configuration Profile is about besides the most recent kernel after which reboot your Linode. If you’re not capable of replace to a patched kernel instantly, you’ll be able to quickly mitigate the difficulty by  eradicating the SUID-bit from pkexec:

# chmod 0755 /usr/bin/pkexec

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