CVE-2026-89825: Linux Kernel Privilege Escalation Vulnerability

CVE-2026-89825 Overview

CVE-2026-89825 is a bounds-check vulnerability in the Linux kernel's drm/panthor driver, which supports Arm Mali GPUs based on the Command Stream Frontend (CSF) architecture. The functions panthor_init_cs_iface() and panthor_init_csg_iface() validate firmware control interface offsets using 32-bit arithmetic and check against the size of host wrapper structures rather than the actual firmware control interface size. Firmware-provided strides can cause the 32-bit arithmetic to wrap before the bounds check completes, allowing out-of-bounds memory access during driver initialization.

Critical Impact
A local attacker with low privileges can trigger memory corruption in the kernel's GPU driver, leading to loss of confidentiality, integrity, and availability on affected systems.

Affected Products

Linux kernel with the drm/panthor driver enabled
Systems using Arm Mali GPUs based on the CSF architecture (for example, Mali-G610)
Distributions shipping vulnerable kernel versions prior to the fix commits

Discovery Timeline

2026-09-16 - CVE-2026-89825 published to the National Vulnerability Database (NVD)
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-89825

Vulnerability Analysis

The panthor driver initializes per-command-stream (CS) and per-command-stream-group (CSG) interfaces by reading stride and count values supplied by GPU firmware. In the vulnerable code path, panthor_init_cs_iface() and panthor_init_csg_iface() compute the offset of each interface using 32-bit multiplication and addition. Because firmware-supplied strides are attacker-influenceable in scenarios where firmware integrity is not guaranteed, the arithmetic can wrap around before the bounds check runs.

The bounds check itself compares the computed offset against the size of the host wrapper structure rather than the size of the firmware control interface region being mapped. This mismatch means offsets that appear valid pass the check but reference memory outside the intended shared firmware region. The result is out-of-bounds read or write access within the kernel address space during driver setup.

The fix, applied across kernel commits 33ae558, 3e5c7cd, 6a47f9f, and 80c9528, converts the offset arithmetic to 64-bit, replaces the wrapper-size comparison with subtraction-based bounds checks against the actual firmware interface structure sizes, and validates that the shared section is large enough to hold the global control interface before use.

Root Cause

The root cause is an integer overflow combined with an incorrect bounds reference. The driver used 32-bit arithmetic on values derived from firmware, and it compared results against the wrong structure size. Both issues fall under improper input validation and numeric truncation error categories in the kernel driver initialization path.

Attack Vector

Exploitation requires local access with low privileges and no user interaction. An attacker needs the ability to influence the values the panthor driver reads during initialization or to trigger reinitialization paths that consume attacker-controlled stride data. Successful exploitation causes kernel memory corruption, which can escalate to arbitrary code execution in kernel context.

No public proof-of-concept exploit is available, and CVE-2026-89825 is not listed in the CISA Known Exploited Vulnerabilities catalog. Technical details are available in the Kernel Git Commit 33ae558 and companion patches.

Detection Methods for CVE-2026-89825

Indicators of Compromise

Unexpected kernel oops or panic messages referencing panthor_init_cs_iface or panthor_init_csg_iface in dmesg output
GPU driver initialization failures or repeated reload attempts on systems with Arm Mali CSF hardware
Kernel address sanitizer (KASAN) reports flagging out-of-bounds access in the drm/panthor module

Detection Strategies

Inventory running kernel versions against the fix commits (33ae558, 3e5c7cd, 6a47f9f, 80c9528) to identify unpatched hosts
Enable KASAN and kernel lockdown on test builds to surface out-of-bounds accesses in the panthor initialization path
Correlate GPU driver load events with subsequent kernel warnings using centralized log collection

Monitoring Recommendations

Forward dmesg and journalctl -k output from Linux hosts with Mali GPUs to a SIEM for anomaly review
Alert on kernel module load failures or unexpected reloads of the panthor module
Track process behavior around unprivileged users interacting with /dev/dri/* device nodes on affected hardware

How to Mitigate CVE-2026-89825

Immediate Actions Required

Update the Linux kernel to a version containing the panthor bounds-check fix from the referenced stable commits
Restrict local access on systems with Arm Mali CSF GPUs until patches are deployed
Audit /dev/dri/renderD* permissions so only trusted users and services can open the panthor device

Patch Information

The fix is committed to the mainline and stable kernel trees. Apply distribution kernel updates that include commits 33ae558, 3e5c7cd, 6a47f9f, and 80c9528. Reboot after patching so the updated kernel and driver take effect.

Workarounds

Blacklist the panthor module on hosts that do not require Arm Mali CSF GPU acceleration
Deny non-root access to DRI render nodes through udev rules or group membership changes
Use verified firmware images for Mali GPUs to reduce the risk of attacker-influenced stride values

bash

# Configuration example: blacklist panthor until the kernel is patched
echo "blacklist panthor" | sudo tee /etc/modprobe.d/blacklist-panthor.conf
sudo update-initramfs -u
sudo reboot