CVE-2020-10757: Linux Kernel Privilege Escalation Flaw

CVE-2020-10757 Overview

A memory corruption vulnerability was discovered in the Linux Kernel affecting versions after 4.5-rc1. The flaw exists in the way mremap handles DAX (Direct Access) Huge Pages, allowing improper memory boundary operations that can lead to privilege escalation. A local attacker with access to a DAX-enabled storage device can exploit this vulnerability to gain elevated privileges on the affected system.

Critical Impact

Local privilege escalation vulnerability allowing attackers with DAX storage access to gain full system control through improper memory remapping operations.

Affected Products

• Linux Linux Kernel (versions after 4.5-rc1)
• Red Hat Enterprise Linux 7.0 and 8.0
• Red Hat Enterprise MRG 2.0
• openSUSE Leap 15.1
• Fedora 31
• Debian Linux 8.0
• Canonical Ubuntu Linux 16.04 ESM, 18.04 LTS, 20.04 LTS
• NetApp Active IQ Unified Manager, Cloud Backup, SteelStore Cloud Integrated Storage

Discovery Timeline

• June 4, 2020 - Vulnerability publicly disclosed via Openwall OSS Security Post
• June 9, 2020 - CVE-2020-10757 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-10757

Vulnerability Analysis

This vulnerability stems from improper handling of DAX Huge Pages during memory remapping operations within the Linux Kernel. DAX (Direct Access) is a feature that allows applications to access persistent memory directly without going through the traditional page cache, enabling faster I/O operations. When combined with Huge Pages (memory pages larger than the standard 4KB), the kernel's mremap system call fails to properly validate and handle memory boundaries.

The flaw allows a local attacker who has access to DAX-enabled storage (such as Intel Optane or other persistent memory devices) to manipulate memory mappings in a way that corrupts kernel memory structures. This memory corruption can be leveraged to achieve privilege escalation, potentially gaining root access on the affected system.

Root Cause

The root cause is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The mremap function in the Linux Kernel does not correctly enforce memory boundaries when handling DAX Huge Pages. This results in improper memory operations that can lead to out-of-bounds memory access or corruption of adjacent memory regions. The vulnerability specifically affects the interaction between the DAX subsystem and the Huge Pages memory management component.

Attack Vector

The attack requires local access to the system and the ability to interact with DAX-enabled storage devices. An attacker must have at least low-level privileges to mount and access DAX filesystems. The attack flow involves:

1. The attacker gains access to a DAX-enabled storage device on the target system
2. A specially crafted memory mapping is created using mmap with DAX Huge Pages
3. The mremap system call is invoked to manipulate the memory region boundaries
4. Improper boundary handling corrupts kernel memory structures
5. The memory corruption is leveraged to escalate privileges to root

The vulnerability can be exploited without user interaction and impacts the confidentiality, integrity, and availability of the affected system.

Detection Methods for CVE-2020-10757

Indicators of Compromise

• Unusual mremap system calls targeting DAX-mapped memory regions
• Unexpected privilege changes for processes interacting with DAX filesystems
• Kernel panic or system instability related to memory management operations
• Suspicious processes accessing DAX-enabled storage devices with elevated permissions

Detection Strategies

• Monitor system calls using auditd or similar tools for unusual mremap operations on DAX filesystems
• Implement kernel-level monitoring to detect anomalous memory mapping patterns
• Use SentinelOne's behavioral AI to detect privilege escalation attempts following DAX filesystem interactions
• Deploy file integrity monitoring on critical DAX-mounted storage areas

Monitoring Recommendations

• Enable kernel auditing for memory-related system calls (mremap, mmap, munmap)
• Configure alerts for unexpected privilege elevation events
• Monitor DAX filesystem mount operations and access patterns
• Implement continuous kernel integrity verification using SentinelOne Singularity platform

How to Mitigate CVE-2020-10757

Immediate Actions Required

• Apply the latest kernel security patches from your distribution vendor immediately
• Restrict access to DAX-enabled storage devices to trusted users only
• Consider disabling DAX functionality if not required for production workloads
• Audit user access permissions for systems with persistent memory hardware

Patch Information

The Linux Kernel developers have addressed this vulnerability through commit 5bfea2d9b17f1034a68147a8b03b9789af5700f9. This patch corrects the boundary handling in mremap for DAX Huge Pages. The fix is available in the upstream Linux kernel and has been backported to various distribution kernels.

Multiple vendors have released security updates:

• Red Hat Bug Report #1842525
• Ubuntu Security Notice #4426
• Debian Security Advisory #4698
• openSUSE Security Announcement
• NetApp Security Advisory

Workarounds

• Disable DAX support by removing the dax mount option from affected filesystems
• Restrict access to DAX devices using filesystem permissions and SELinux/AppArmor policies
• Implement strict user access controls to limit who can interact with persistent memory devices
• Consider using containers or virtual machines to isolate workloads requiring DAX functionality

# Remove DAX mount option from fstab
# Before: /dev/pmem0 /mnt/pmem ext4 dax,defaults 0 0
# After:  /dev/pmem0 /mnt/pmem ext4 defaults 0 0

# Remount filesystem without DAX
sudo umount /mnt/pmem
sudo mount -o defaults /dev/pmem0 /mnt/pmem

# Restrict access to pmem devices
sudo chmod 600 /dev/pmem*
sudo chown root:root /dev/pmem*