CVE-2026-68277 Overview
CVE-2026-68277 is an out-of-bounds read vulnerability in the Linux kernel's Direct Rendering Manager (DRM) DisplayPort Multi-Stream Transport (MST) subsystem. Three sideband reply parsers read 16-bit fields without validating the index before dereferencing the second byte. When the index equals the received message length (raw->curlen), the parser reads one byte past the message buffer into adjacent struct fields.
Critical Impact
An attacker able to inject or manipulate DisplayPort MST sideband replies can trigger a one-byte out-of-bounds read, causing information disclosure or driver misbehavior in the kernel.
Affected Products
- Linux kernel DRM DisplayPort MST subsystem
- Systems using DisplayPort Multi-Stream Transport hub or daisy-chained displays
- Distributions shipping the affected drm/dp/mst code prior to the fix
Discovery Timeline
- 2026-08-10 - CVE-2026-68277 published to NVD
- 2026-08-10 - Last updated in NVD database
Technical Details for CVE-2026-68277
Vulnerability Analysis
The vulnerability resides in three sideband reply parser functions within the DRM DisplayPort MST driver: drm_dp_sideband_parse_enum_path_resources_ack(), drm_dp_sideband_parse_allocate_payload_ack(), and drm_dp_sideband_parse_query_payload_ack(). Each function reads a 16-bit big-endian value from the message buffer using the pattern val = (raw->msg[idx] << 8) | (raw->msg[idx+1]) and only validates the index against raw->curlen after the read completes.
Affected fields include full_payload_bw_number and avail_payload_bw_number in the enumerate path resources parser, and the allocated_pbn field in both the allocate payload and query payload parsers. When idx equals raw->curlen, the parser reads raw->msg[idx+1], which lies one byte past the valid message data.
Root Cause
The root cause is a boundary condition error where bounds checks occur after memory access rather than before. The check idx > curlen fails to prevent the second byte read when idx == curlen. The overread lands in the following struct members (curchunk_len, curchunk_idx, curlen), producing attacker-influenced values that flow into bandwidth and payload calculations.
Attack Vector
Exploitation requires the ability to deliver a crafted DisplayPort MST sideband reply to the kernel parser. This can occur through a malicious or compromised MST hub, a physically connected malicious display device, or any component along the DisplayPort link that can shape sideband responses. The parser processes the reply and reads one byte beyond the intended buffer boundary, exposing adjacent kernel memory contents to the parsing logic.
The fix introduces a combined bounds check (idx + 2 > curlen) before each 2-byte read. This check is strictly tighter than the previous idx > curlen verification, so no additional step is required after the read.
Detection Methods for CVE-2026-68277
Indicators of Compromise
- Unexpected DisplayPort MST bandwidth or payload values reported by the kernel that do not correspond to attached hardware capabilities
- Kernel log entries from the drm/dp/mst subsystem showing malformed sideband replies or truncated messages
- Presence of untrusted DisplayPort hubs or docks in environments where physical access is not restricted
Detection Strategies
- Audit installed kernel versions against the upstream stable commits 0bcd7675, 68a62441, 6b89ba3d, bdf0508b, and d5c70523 to identify unpatched systems
- Monitor dmesg and kernel ring buffer output for anomalous DRM DisplayPort MST parser activity following display hot-plug events
- Correlate DisplayPort topology change events with kernel warnings on endpoints exposed to unmanaged peripherals
Monitoring Recommendations
- Track kernel package inventory and patch state across Linux endpoints and servers with graphical output
- Log and review peripheral connection events for docking stations, KVMs, and MST hubs in sensitive environments
- Watch for repeated display link resets or MST topology rebuilds that may indicate probing of the sideband parser
How to Mitigate CVE-2026-68277
Immediate Actions Required
- Apply the upstream Linux kernel patches referenced by commits 0bcd7675c69a, 68a624416d1d, 6b89ba3dba2f, bdf0508b1e67, and d5c70523cafa as delivered by your distribution
- Update to the latest stable kernel release provided by your Linux vendor that includes the DRM DisplayPort MST fix
- Restrict physical access to DisplayPort ports on kiosks, shared workstations, and unattended systems
Patch Information
The fix is available in the mainline Linux kernel and backported stable branches. Reference the following commits for the corrected 2-byte bounds check: Kernel Git Commit 0bcd7675, Kernel Git Commit 68a6244, Kernel Git Commit 6b89ba3, Kernel Git Commit bdf0508, and Kernel Git Commit d5c7052.
Workarounds
- Disable DisplayPort MST support in firmware or graphics driver configuration where multi-stream topologies are not required
- Use only trusted, vendor-supplied DisplayPort docks, hubs, and displays in high-assurance environments
- Enforce endpoint policies that alert on new USB-C or DisplayPort peripheral attachments on sensitive hosts
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
