CVE-2026-53135: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-53135 Overview

CVE-2026-53135 affects the Linux kernel's AMD display driver (drm/amd/display). The flaw resides in the dp_sdp_message_debugfs_write() function, which dereferences connector->base.state->crtc without a NULL check. A connector can be connected but not bound to any CRTC, such as after a hot-plug event before the next atomic commit. Writing to the sdp_message debugfs node in this state triggers a kernel crash. The same function ignores the user-provided size argument and always passes 36 bytes to copy_from_user(), reading past the user buffer when the supplied size is smaller. The issue has been resolved upstream and backported to stable kernel branches.

Critical Impact
Local users with access to the AMD display debugfs interface can crash the kernel through a NULL pointer dereference or trigger an out-of-bounds read from user memory.

Affected Products

Linux kernel — drm/amd/display driver
Stable kernel branches receiving the cherry-picked fix from commit 6ab4c36a522842ff70474a1c0af2e40e50fc8300
Systems exposing the sdp_message debugfs node on AMD GPUs

Discovery Timeline

2026-06-25 - CVE-2026-53135 published to NVD
2026-06-25 - Last updated in NVD database

Technical Details for CVE-2026-53135

Vulnerability Analysis

The defect lives in dp_sdp_message_debugfs_write() inside the AMD Display Port (DP) Secondary Data Packet (SDP) debugfs handler. The function performs two unsafe operations on a single write path. First, it accesses connector->base.state->crtc without verifying that either connector->base.state or state->crtc is non-NULL. Second, it hardcodes a 36-byte transfer to copy_from_user() regardless of the caller-supplied size argument. The combination produces both a denial-of-service primitive and an out-of-bounds read of process memory.

Root Cause

The root cause is missing input validation on kernel state pointers and missing bounds clamping on a user-controlled length. A DP connector may report as connected immediately after a hot-plug event yet remain unbound to a CRTC until the next atomic modeset commit. Code that assumes a CRTC is always attached dereferences a NULL pointer in this transient window. The fixed-size copy_from_user() ignores the contract that callers may write fewer bytes than the buffer can hold, producing an out-of-bounds read [CWE-125, CWE-476].

Attack Vector

Exploitation requires local access to the debugfs interface, which is typically restricted to privileged users. An attacker with write permission to /sys/kernel/debug/dri/*/sdp_message issues a write while the targeted DP connector is in the connected-but-unbound state. The handler then dereferences a NULL crtc pointer and panics the kernel. Alternatively, an attacker submits a write smaller than 36 bytes to force the handler to read past the user buffer boundary.

The upstream patch returns -ENODEV when connector->base.state or state->crtc is NULL and clamps the write length to min(size, sizeof(data)). The fix is recorded in kernel commits 7ae95c02, 7fc4fab4, a2de1d71, adf67034, b781f90a, bb6f705b, c90954cd, and ee9cfcf7.

Detection Methods for CVE-2026-53135

Indicators of Compromise

Kernel oops or panic traces referencing dp_sdp_message_debugfs_write in dmesg or /var/log/kern.log
Unexpected writes to /sys/kernel/debug/dri/*/sdp_message from non-administrative processes
DRM subsystem stack traces referencing NULL pointer dereferences during DisplayPort hot-plug activity

Detection Strategies

Monitor kernel logs for crash signatures involving the AMD display driver and SDP debugfs handlers
Audit access controls on the debugfs mount and confirm it is mounted with restrictive permissions (mode=700)
Inventory hosts running AMD GPUs with vulnerable kernel versions and confirm patch level against the stable branches

Monitoring Recommendations

Forward kernel ring buffer events to a centralized log platform and alert on BUG: or Oops: strings tied to drm/amd/display
Track auditd events for open() and write() syscalls on debugfs paths under /sys/kernel/debug/dri/
Correlate kernel crashes with DisplayPort hot-plug events to identify exploitation attempts in the connected-but-unbound window

How to Mitigate CVE-2026-53135

Immediate Actions Required

Apply the upstream Linux kernel patch by upgrading to a stable kernel release containing the referenced commits
Restrict access to debugfs by ensuring it is mounted with root-only permissions or unmounted on production systems that do not require it
Identify and prioritize systems running AMD GPUs with kernels predating the fix

Patch Information

The fix was cherry-picked from upstream commit 6ab4c36a522842ff70474a1c0af2e40e50fc8300 and propagated to multiple stable branches. Distribution kernels should pick up the change through the standard stable update process. Reference the Kernel Commit 7ae95c02, Kernel Commit 7fc4fab4, Kernel Commit a2de1d71, Kernel Commit adf67034, Kernel Commit b781f90a, Kernel Commit bb6f705b, Kernel Commit c90954cd, and Kernel Commit ee9cfcf7 for the exact source changes.

Workarounds

Unmount debugfs on production hosts that do not require it: umount /sys/kernel/debug
Restrict debugfs mount permissions so only root can traverse the hierarchy
Remove write permission on /sys/kernel/debug/dri/*/sdp_message for non-root users until the patched kernel is deployed

bash

# Configuration example - restrict debugfs access until patched kernel is installed
mount -o remount,mode=700 /sys/kernel/debug

# Verify current kernel version against patched stable branches
uname -r