Netfilter Firewall Module Linux Bug Permits Access to Gain Root

  • By Patrick Ryan
  • Mar 18, 2022

Digital criminals are taking advantage of a Linux bug within a netfilter firewall module to gain root access. The digital security vulnerability within the Linux kernel can be compromised through a local adversary looking to secure elevated privileges on susceptible systems. Opportunistic hackers will use those elevated privileges to execute escape containers, arbitrary code, and worse. Hackers might also use the bug to spur a kernel panic.

What Versions of Linux are Affected?

Referred to as CVE-2022-25636, the vulnerability is found within Linux kernel version 5.4 through 5.6.10. The kernel stems from a write within the kernel’s subcomponent netfilter referred to as heap out-of-bounds. A Sophos digital security specialist named Nick Gregory discovered the flaw.

Why is the Bug a Problem?

The flaw empowers local attackers to take advantage of a user account on the target system to obtain access to memory that is out-of-bounds, spurring a privilege escalation threat or a full system crash. The vulnerability centers on problems with the handling of the hardware offload feature of the framework that has the potential to be used as weapons to trigger the execution of arbitrary code or denial-of-service.

The bug is catalyzed prior to the failure of rule creation, leading to the escalation of local privileges within kernels. Hackers find it quite convenient that one of the values written out of bounds serves as a form of redirection to net device structures.

The bug can set the stage for kernel code execution with return-oriented programming that permits the full escalation of local privileges, meaning an outside party can control the target’s computer. The problem occurs because of netfilter failing to properly handle the functionality of hardware offloads. The vulnerability can function even if the targeted hardware lacks the offload feature.

What is Netfilter all About?

Netfilter is an essential security program within Linux that empowers users to execute operations related to networking, including network address translation, port translation, packet filtering, userspace packet queues, and packet logging.  

Kernel code execution can be performed with ROP, short for return-oriented programming, setting the stage for full local privilege access. The failure to properly manage hardware offload functionality spurs the underlying issue, allowing for the flaw’s exploitation and a subsequent denial-of-service, the use of arbitrary code, and additional harmful activities.

What Can be Done to Combat the Digital Security Flaw?

Though a patch for the Linux kernel netfilter has been developed, the patch has not yet been made available within distribution releases. The use of Linux 8 Red Hat Enterprise with the disabling of unprivileged users can mitigate the issue. However, if it is impossible to deactivate user namespaces, container mitigation can be implemented to thwart syscalls within seccomp policy files.  

Businesses and individuals with computers that have the Linux operating system are also encouraged to implement overarching digital security protections to guard against the threat described above and additional cybercriminal activity. 

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