CVE-2020-10757: Linux Kernel Privilege Escalation Flaw

CVE-2020-10757 Overview

CVE-2020-10757 is a Linux kernel flaw affecting versions after 4.5-rc1 in the way mremap handled Direct Access (DAX) Huge Pages. A local attacker with access to DAX-enabled storage can exploit this flaw to escalate privileges on the affected system. The vulnerability is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and was patched upstream via commit 5bfea2d9b17f1034a68147a8b03b9789af5700f9. Major Linux distributions including Red Hat Enterprise Linux, Ubuntu, Debian, openSUSE, and Fedora released coordinated security updates. NetApp products bundling vulnerable kernel components were also affected.

Critical Impact
A local user with DAX-enabled storage access can escalate to root on unpatched Linux systems running kernel versions after 4.5-rc1.

Affected Products

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

Discovery Timeline

2020-06-09 - CVE-2020-10757 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-10757

Vulnerability Analysis

The flaw resides in the Linux kernel memory management subsystem, specifically in how the mremap system call processes DAX Huge Pages. DAX (Direct Access) allows file systems on persistent memory devices to bypass the page cache and map storage directly into a process address space. When mremap operates on mappings backed by DAX huge pages, the kernel fails to properly handle the page table entries.

This results in improper memory boundary handling [CWE-119], allowing a local attacker to manipulate memory regions outside the intended scope. The defect enables a user-mode process to gain access to kernel-managed memory or escalate privileges to root. Exploitation requires local access and the ability to interact with DAX-enabled storage, which is typically used in high-performance computing and storage workloads involving persistent memory (NVDIMM) devices.

Root Cause

The upstream commit 5bfea2d9b17f1034a68147a8b03b9789af5700f9 corrects the handling logic for DAX huge page mappings during mremap operations. The original code path did not properly validate or relocate page table entries for huge pages on DAX-backed memory, leading to inconsistent state between page tables and physical mappings.

Attack Vector

Exploitation is local and requires a valid account on the target system plus access to a DAX-enabled storage device. The attacker crafts a sequence of mmap and mremap calls against a DAX huge page mapping to trigger the flawed page table manipulation. No user interaction is required, and successful exploitation grants attacker-controlled access to privileged memory, leading to full root compromise. The vulnerability mechanism is documented in the Red Hat Bug Report #1842525 and the Linux Kernel Commit 5bfea2d.

Detection Methods for CVE-2020-10757

Indicators of Compromise

Unexpected root-privileged processes spawned from non-privileged user sessions on systems with NVDIMM or persistent memory devices.
Kernel log entries (dmesg) showing page table corruption, oops messages, or unusual DAX-related warnings.
Processes performing unusual mremap syscall patterns against files on DAX-mounted filesystems (e.g., ext4 or XFS mounted with -o dax).

Detection Strategies

Audit kernel versions across the fleet and flag any host running a Linux kernel after 4.5-rc1 without the vendor-supplied patch.
Enable Linux audit rules (auditd) targeting the mremap syscall and correlate with subsequent privilege transitions to UID 0.
Monitor for filesystems mounted with the dax option using configuration management or endpoint telemetry.

Monitoring Recommendations

Collect kernel version inventory continuously and compare against vendor advisories such as Ubuntu Security Notice USN-4426-1 and Debian Security Advisory DSA-4698.
Forward auditd, dmesg, and process execution telemetry to a centralized analytics platform for behavioral baselining.
Alert on local privilege escalation patterns: short-lived child processes that inherit elevated credentials from non-privileged parents.

How to Mitigate CVE-2020-10757

Immediate Actions Required

Apply the kernel security update from your distribution vendor and reboot affected systems to load the patched kernel.
Identify hosts using DAX-enabled storage and prioritize them for patching, as they represent the exploitable population.
Restrict local shell access on affected systems until patches are deployed, particularly for untrusted users.

Patch Information

The upstream fix is included in commit 5bfea2d9b17f1034a68147a8b03b9789af5700f9 in the mainline Linux kernel. Distribution-specific patches are available in Ubuntu Security Notice USN-4426-1, Ubuntu Security Notice USN-4439-1, Ubuntu Security Notice USN-4440-1, Ubuntu Security Notice USN-4483-1, Debian Security Advisory DSA-4698, Debian Security Advisory DSA-4699, the openSUSE Security Announcement, the Fedora Package Announcement, and NetApp Security Advisory NTAP-20200702-0004.

Workarounds

Remount affected filesystems without the dax option where the performance trade-off is acceptable, eliminating the exploit prerequisite.
Limit access to DAX-enabled storage devices through filesystem permissions and Linux capabilities.
Disable interactive local logins for non-administrative users on hosts where patching cannot be performed immediately.

bash

# Verify kernel version and DAX-mounted filesystems
uname -r
mount | grep -i dax

# Remove the dax mount option (example for /etc/fstab)
# Change: /dev/pmem0 /mnt/pmem ext4 defaults,dax 0 0
# To:     /dev/pmem0 /mnt/pmem ext4 defaults      0 0

# Apply distribution updates
# Ubuntu / Debian
sudo apt-get update && sudo apt-get install --only-upgrade linux-image-generic
# Red Hat / Fedora
sudo dnf update kernel
# openSUSE
sudo zypper patch

# Reboot to load patched kernel
sudo systemctl reboot