CVE-2026-68088 Overview
CVE-2026-68088 is a vulnerability in the Linux kernel's USB gadget subsystem. The flaw resides in the Remote Network Driver Interface Specification (RNDIS) function driver, specifically in the rndis_query_response() handler. The function previously processed BufLength and BufOffset parameters from RNDIS query messages without proper bounds validation. The upstream fix introduces variable representations for these fields and applies a length check identical to the one already present in rndis_set_response(). This inconsistency between the two response handlers created an input validation gap that could be reached through the USB gadget interface.
Critical Impact
Missing bounds validation on attacker-controlled RNDIS query parameters can allow out-of-bounds memory access in the Linux kernel USB gadget driver.
Affected Products
- Linux kernel — USB gadget RNDIS function driver (drivers/usb/gadget/function/rndis.c)
- Multiple stable kernel branches (fixes backported across eight stable trees)
- Devices operating in USB gadget mode using RNDIS (Android tethering, embedded Linux boards, IoT devices)
Discovery Timeline
- 2026-08-10 - CVE-2026-68088 published to NVD
- 2026-08-13 - Last updated in NVD database
Technical Details for CVE-2026-68088
Vulnerability Analysis
RNDIS is a Microsoft-defined protocol used to expose network devices over USB. The Linux kernel implements the device-side RNDIS control plane in the USB gadget function driver. When a host sends a REMOTE_NDIS_QUERY_MSG, the gadget parses the message and dispatches it to rndis_query_response(). This handler reads InformationBufferLength (BufLength) and InformationBufferOffset (BufOffset) fields from the incoming message. Prior to the fix, the values were consumed without verifying they lay within the bounds of the received buffer. The sibling function rndis_set_response() already contained the required validation, so the patch aligns both handlers on the same defensive check. Missing input validation in a kernel-mode USB message parser is classified under improper input validation and can lead to out-of-bounds reads.
Root Cause
The root cause is missing input validation on protocol-supplied length and offset fields. rndis_query_response() trusted BufLength and BufOffset from the RNDIS message header without confirming that BufOffset + BufLength remained inside the received control message. Any check performed elsewhere in the code path was insufficient for the query response path.
Attack Vector
An attacker with the ability to send crafted RNDIS control messages to a Linux device operating in USB gadget mode can trigger the flaw. This typically requires physical USB access to the target, or control over a host that a device connects to. Successful exploitation reads memory beyond the intended buffer inside kernel context, producing information disclosure or a kernel crash depending on adjacent memory layout.
No public proof-of-concept or exploit is currently associated with this CVE. See the upstream commits for the exact patch content: b09716040f3f and efcf4e4eeea0.
Detection Methods for CVE-2026-68088
Indicators of Compromise
- Unexpected kernel warnings or oops entries referencing rndis_query_response in dmesg or /var/log/kern.log.
- USB gadget devices disconnecting or resetting after receiving RNDIS control traffic from an untrusted host.
- Anomalous RNDIS query messages where InformationBufferOffset + InformationBufferLength exceeds the message length reported by the host.
Detection Strategies
- Inventory Linux systems running in USB gadget mode with g_ether, g_multi, or other configurations that expose RNDIS, and compare kernel versions against the patched stable releases.
- Enable kernel address sanitizer (KASAN) on test devices to surface out-of-bounds reads in rndis_query_response() during fuzzing.
- Monitor for repeated USB gadget driver faults on production embedded devices; correlate with USB reconnection events.
Monitoring Recommendations
- Ship kernel logs from embedded and mobile fleets to a central data lake and alert on rndis-scoped warnings, oopses, or panics.
- Track kernel package versions across the fleet and flag hosts still running pre-patch stable branches.
- Baseline expected USB peripheral behavior on kiosks and industrial devices; alert on unexpected RNDIS query volumes.
How to Mitigate CVE-2026-68088
Immediate Actions Required
- Upgrade to a stable Linux kernel release that includes one of the merged fixes referenced in the NVD entry.
- Rebuild and redeploy custom kernels for embedded and IoT devices to pick up the corrected rndis_query_response() handler.
- On devices that do not require USB tethering, disable the RNDIS gadget function or unload the corresponding module.
Patch Information
The fix is distributed across eight stable-tree commits, including 585921866d2d, 95f90eea0708, b09716040f3f, bb2b4402b457, caea8b120604, e01e7814b422, efcf4e4eeea0, and f5870777458d. Apply the commit corresponding to your stable branch.
Workarounds
- Disable the RNDIS USB gadget function on devices where it is not required for operation.
- Restrict physical USB access to production devices, particularly kiosks, medical equipment, and industrial controllers that expose gadget interfaces.
- Where feasible, prefer alternate USB networking functions such as CDC-ECM or CDC-NCM over RNDIS.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
