CVE-2020-7053: Linux Kernel Use-After-Free Vulnerability

CVE-2020-7053 Overview

CVE-2020-7053 is a use-after-free (write) vulnerability in the Linux kernel's Intel i915 graphics driver. The flaw exists in the i915_ppgtt_close function within drivers/gpu/drm/i915/i915_gem_gtt.c and is related to improper memory handling in i915_gem_context_destroy_ioctl in drivers/gpu/drm/i915/i915_gem_context.c. This vulnerability affects multiple longterm kernel versions including 4.14 through 4.14.165, 4.19 through 4.19.96, and 5.x versions before 5.2.

Critical Impact

Local attackers with low privileges can exploit this use-after-free vulnerability to potentially achieve arbitrary code execution, compromise system confidentiality, integrity, and availability on systems with Intel integrated graphics.

Affected Products

• Linux Kernel 4.14 longterm through 4.14.165
• Linux Kernel 4.19 longterm through 4.19.96
• Linux Kernel 5.x before 5.2

Discovery Timeline

• 2020-01-14 - CVE-2020-7053 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-7053

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption flaw where the application references memory after it has been freed. The vulnerable code path involves the Intel i915 graphics driver's page table management, specifically in how graphics execution contexts are destroyed.

When a graphics context is destroyed via the i915_gem_context_destroy_ioctl function, there is a race condition or improper ordering of operations that can lead to the i915_ppgtt_close function accessing memory that has already been deallocated. Since this is a use-after-free write condition, an attacker could potentially manipulate the freed memory region before it is accessed, allowing for arbitrary memory corruption.

The vulnerability requires local access and low privileges, meaning an attacker must have some level of access to the target system. However, no user interaction is required for exploitation. Successful exploitation could allow an attacker to execute arbitrary code with kernel privileges, leading to complete system compromise.

Root Cause

The root cause of CVE-2020-7053 lies in improper lifetime management of Per-Process Graphics Translation Tables (PPGTT) within the Intel i915 Direct Rendering Manager (DRM) driver. When a GEM (Graphics Execution Manager) context is destroyed, the associated PPGTT structures are not properly tracked, leading to a scenario where i915_ppgtt_close can reference memory after it has been freed during context destruction.

The fix, identified by commit 7dc40713618c884bf07c030d1ab1f47a9dc1f310, addresses this by ensuring proper synchronization and ordering of memory deallocation operations in the graphics context teardown path.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to have existing access to the target system. The exploitation scenario involves:

1. An attacker with local user-level access creates and manipulates graphics contexts through the i915 driver's ioctl interface
2. By carefully timing context destruction operations, the attacker triggers the use-after-free condition
3. The freed memory is reallocated with attacker-controlled content before the dangling reference is accessed
4. When i915_ppgtt_close writes to the freed memory location, it corrupts the attacker-controlled data structure
5. This memory corruption can be leveraged for privilege escalation or arbitrary code execution in kernel context

The vulnerability is triggered through the standard DRM ioctl interface, making it accessible to any local user with access to the graphics device.

Detection Methods for CVE-2020-7053

Indicators of Compromise

• Unexpected kernel panics or crashes related to the i915 DRM driver
• Kernel log messages (dmesg) showing memory corruption errors in i915_ppgtt_close or i915_gem_context_destroy_ioctl
• Unusual activity involving graphics context creation and destruction operations
• Signs of privilege escalation from low-privileged user accounts

Detection Strategies

• Monitor kernel logs for i915 driver-related errors, particularly memory access violations or use-after-free warnings from kernel address sanitizer (KASAN)
• Implement system call auditing to track ioctl calls to /dev/dri/card* devices, especially context destruction operations
• Deploy kernel live patching solutions such as those mentioned in the Packet Storm Security Notice to detect and prevent exploitation attempts
• Use SentinelOne's behavioral AI to detect unusual patterns of graphics driver interactions that may indicate exploitation attempts

Monitoring Recommendations

• Enable kernel auditing (auditd) for DRM ioctl operations on systems with Intel integrated graphics
• Monitor for suspicious processes making repeated graphics context create/destroy calls
• Implement memory corruption detection mechanisms such as KASAN in development/testing environments
• Deploy endpoint detection solutions capable of monitoring kernel-level activity for signs of exploitation

How to Mitigate CVE-2020-7053

Immediate Actions Required

• Update the Linux kernel to version 5.2 or later, which contains the fix for this vulnerability
• For systems running 4.14 longterm, upgrade to version 4.14.166 or later
• For systems running 4.19 longterm, upgrade to version 4.19.97 or later
• Apply vendor-specific patches from Ubuntu, openSUSE, or other distributions as documented in their security advisories

Patch Information

The vulnerability has been addressed in the upstream Linux kernel through commit 7dc40713618c884bf07c030d1ab1f47a9dc1f310. This fix is documented in the Linux Kernel ChangeLog 5.2 and has been backported to stable kernel branches.

Multiple Linux distributions have released security updates addressing this vulnerability:

• Ubuntu: USN-4255-1, USN-4255-2, USN-4285-1, USN-4287-1, USN-4287-2
• openSUSE: openSUSE Security Announcement
• NetApp: NTAP-20200204-0002

For detailed patch information, refer to the Linux Kernel Commit 7dc4071.

Workarounds

• If immediate patching is not possible, consider restricting access to /dev/dri/* devices to trusted users only
• Implement kernel live patching solutions to apply fixes without system reboots
• Use security modules like SELinux or AppArmor to restrict graphics driver access for untrusted applications
• Monitor and audit all access to DRM device nodes on affected systems

# Restrict access to DRM devices (temporary mitigation)
# Only allow members of 'video' group to access graphics devices
chmod 660 /dev/dri/card*
chown root:video /dev/dri/card*

# Verify current kernel version
uname -r

# Check if i915 module is loaded
lsmod | grep i915

# Apply kernel updates (Ubuntu example)
sudo apt update && sudo apt upgrade linux-image-generic