CVE-2026-68279: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-68279 Overview

CVE-2026-68279 is an out-of-bounds read vulnerability in the Linux kernel's DisplayPort Multi-Stream Transport (MST) sideband message parsers. The flaw resides in drm_dp_sideband_parse_remote_dpcd_read() and drm_dp_sideband_parse_remote_i2c_read_ack() within the drm/dp/mst subsystem. Both functions perform memcpy() operations using an attacker-controlled num_bytes value without validating that idx + num_bytes remains within raw->curlen. A malicious or misbehaving MST hub can supply an oversized num_bytes, causing the kernel to read past the received payload into adjacent memory within the 256-byte raw->msg[] buffer.

Critical Impact
A malicious MST hub connected via DisplayPort can trigger kernel out-of-bounds reads, potentially leaking uninitialized kernel memory adjacent to the sideband message buffer.

Affected Products

Linux kernel versions containing the vulnerable drm/dp/mst sideband parser code
Systems using DisplayPort Multi-Stream Transport with the DRM subsystem
Kernel builds prior to the fix commits referenced in the stable tree

Discovery Timeline

2026-08-10 - CVE-2026-68279 published to NVD
2026-08-10 - Last updated in NVD database

Technical Details for CVE-2026-68279

Vulnerability Analysis

The vulnerability affects the Linux kernel DRM (Direct Rendering Manager) DisplayPort MST sideband reply parsing logic. When a downstream MST device sends a remote DPCD (DisplayPort Configuration Data) read reply or a remote I2C read acknowledgment, the kernel parses the response into a raw message buffer of 256 bytes. The parsers extract a num_bytes field from the raw wire data and then invoke memcpy(bytes, &raw->msg[idx], num_bytes) to copy the payload into the caller's output structure.

Neither parser verifies that idx + num_bytes remains within raw->curlen, which represents the actual received payload length. Because num_bytes is a u8, an attacker-controlled hub can specify values up to 255 regardless of how much data was actually received. The memcpy() then reads whatever bytes follow the received data in raw->msg[], exposing stale contents from prior sideband transactions or adjacent memory.

The I2C variant of this flaw was documented with a /* TODO check */ comment in the original commit, indicating the bounds check was known to be missing since introduction. This falls under [CWE-125] Out-of-Bounds Read.

Root Cause

The root cause is missing bounds validation in two sideband reply parsers. Both functions trust the length field encoded in the untrusted sideband message without cross-checking it against the actual received payload size stored in curlen. The fix introduces a combined check (idx + num_bytes > curlen) before each memcpy() invocation, rejecting malformed replies before the out-of-bounds copy occurs.

Attack Vector

Exploitation requires an attacker to control an MST-capable DisplayPort device connected to a vulnerable Linux system. This includes malicious docking stations, MST hubs, or compromised display peripherals. When the kernel initiates a remote DPCD or I2C read against the downstream device, the attacker-controlled hub returns a crafted sideband reply with an inflated num_bytes value. The kernel copies memory beyond the received payload into caller buffers, which may then be surfaced to userspace through DRM ioctls or subsequent processing paths.

The vulnerability primarily enables kernel memory disclosure. Because the leaked bytes originate from the 256-byte raw->msg[] buffer, information disclosure is bounded to data structures colocated with that buffer, including remnants of prior sideband transactions.

The vulnerability manifests in the message-length validation logic. See the Linux kernel stable tree commits referenced below for the exact patch semantics.

Detection Methods for CVE-2026-68279

Indicators of Compromise

Unexpected MST sideband reply messages logged by the DRM subsystem with anomalous length fields
Kernel warnings or KASAN reports referencing drm_dp_sideband_parse_remote_dpcd_read or drm_dp_sideband_parse_remote_i2c_read_ack
Attachment of unrecognized DisplayPort MST hubs or docking stations to sensitive endpoints

Detection Strategies

Enable Kernel Address Sanitizer (KASAN) on test builds to surface out-of-bounds reads in the DRM MST parsers
Audit dmesg output for DRM DP MST parse errors and malformed sideband message warnings
Monitor for physical peripheral connections to endpoints where DisplayPort MST is enabled

Monitoring Recommendations

Collect kernel logs centrally and alert on DRM subsystem errors originating from MST message parsing paths
Track kernel version inventory across the fleet to identify hosts running unpatched builds
Correlate USB-C and DisplayPort device attachment events with subsequent kernel warnings

How to Mitigate CVE-2026-68279

Immediate Actions Required

Apply the upstream Linux kernel patches from the stable tree that add the idx + num_bytes > curlen bounds check
Update to a distribution kernel package that incorporates the fix commits referenced in the Linux stable tree
Restrict physical access to DisplayPort ports on systems handling sensitive data, particularly laptops and workstations that dock frequently

Patch Information

The fix has been merged into the Linux kernel stable tree across multiple branches. Refer to the following commits:

Rebuild affected kernels or install vendor-provided packages containing these fixes, then reboot to activate the patched kernel.

Workarounds

Disable DisplayPort MST support where not required by unloading or blacklisting DRM MST functionality on servers and headless systems
Enforce USB-C and DisplayPort peripheral allowlisting through endpoint device control policies
Physically block unused DisplayPort connectors on high-value endpoints until patches are deployed