External risk intelligence

Android Kernel Privilege Escalation Vulnerability

CVE advisoryKnown Exploit

CVE-2021-0920

A race condition in the Android kernel could allow for privilege escalation. This impacts organizations by enabling unauthorized access to system functions and data on affected systems. Exploitation requires local access and does not need user interaction.

1Halo Surface Signal

Use After Free

Linux Kernel

5.13 and earlier5.149.0

External exposure likelihood

Halo Surface Signal score for CVE-2021-0920

This vulnerability exists within the operating system kernel and requires local access to the system to exploit. It does not involve a network-accessible service, application, or remote interface, making it inherently local and not reachable via the public internet.

Horizon Alert

Summary of the vulnerability and why it matters

A race condition in the Android kernel's Unix domain socket handling could allow for privilege escalation. This flaw exists in the way the system manages memory for socket operations, potentially leading to unauthorized access to sensitive system functions. This could impact organizations by allowing unauthorized users to gain higher levels of control over affected systems.

  • Vulnerable: Android kernel
  • Flaw: Memory use-after-free due to race condition
  • Impact: Privilege escalation on affected systems

Attack Path

How an attacker could exploit the issue

A race condition in the Android kernel's af_unix.c file could allow for privilege escalation. This vulnerability, a use-after-free bug, can be exploited by an attacker with system execution privileges. User interaction is not required for exploitation, meaning an attacker could trigger the vulnerability without user consent.

  • Local system access required
  • Attacker triggers race condition
  • Results in privilege escalation

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker with high skill to escalate privileges on a system. Exploitation requires local access and is not dependent on user interaction. The potential impact includes unauthorized access and modification of sensitive data, posing a significant business risk. Organizations should prioritize addressing this vulnerability.

  • Likely attacker skill level: High.
  • Required access or conditions: Local system access.
  • Business risk or urgency: Significant.

Priority actions

Operational Fix

Recommended remediation, mitigation, and detection steps

A race condition in the Android kernel's Unix domain socket handling could allow for local privilege escalation. This vulnerability, identified within `af_unix.c`, is a use-after-free bug that does not require user interaction to exploit. Organizations should prioritize identifying systems with the affected kernel versions, reducing potential exposure, and applying vendor-provided security updates.

  • Find affected kernel assets.
  • Reduce exposure or isolate risk.
  • Fix, verify, and monitor.

Frequently asked questions

What is the Android kernel and how does CVE-2021-0920 affect it?

The Android kernel is the core component of the Android operating system, managing hardware and software interactions. CVE-2021-0920 is a use-after-free vulnerability within the Linux kernel used by Android. Specifically, it resides in the Unix domain socket handling (`af_unix.c`) and arises from a race condition in the garbage collection system for SCM_RIGHTS, which allows file descriptors to be passed between processes [1, 2, 6, 7, 8, 10, 11, 12].

What type of weakness does CVE-2021-0920 represent?

CVE-2021-0920 represents a use-after-free (UAF) memory corruption vulnerability [1, 2, 5, 8, 9]. This occurs due to a race condition in how the kernel handles socket buffers (sk_buff) when file descriptors are being managed, leading to a situation where memory is accessed after it has been deallocated [1, 2, 6, 10].

How can an attacker trigger CVE-2021-0920 and what is its scope?

An attacker can trigger CVE-2021-0920 by exploiting a race condition during the garbage collection of Unix domain sockets. This typically involves calling the `recvmsg` syscall with the `MSG_PEEK` flag [1]. The vulnerability allows for local privilege escalation, meaning an attacker needs system execution privileges or local system access to exploit it. User interaction is not required for exploitation [4, 5, 8, 10, 12].

Who should be concerned about CVE-2021-0920 and what is its threat level?

Organizations using Android devices with affected kernel versions should be concerned about CVE-2021-0920. This vulnerability has been confirmed as exploited in the wild and is included in CISA's Known Exploited Vulnerabilities Catalog [4, 13, 15]. It carries a medium severity rating (CVSS 3.1 base score of 6.4) and has been used in targeted exploitation campaigns to escape sandboxes and elevate privileges [2, 4, 5].

What is the recommended approach to address CVE-2021-0920?

The primary method to address CVE-2021-0920 is to apply security updates provided by the vendor. Google released patches for this vulnerability in the November 2021 Android Security Bulletin, and affected devices received these updates through subsequent security patches [1, 13]. Organizations should ensure their Android devices are updated to the latest available security patch level.

References