smb: client: fix krb5 mount with username option_CVE-2026-31392

{
    "lastseen": "",
    "description": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix krb5 mount with username option\n\nCustomer reported that some of their krb5 mounts were failing against\na single server as the client was trying to mount the shares with\nwrong credentials.  It turned out the client was reusing SMB session\nfrom first mount to try mounting the other shares, even though a\ndifferent username= option had been specified to the other mounts.\n\nBy using username mount option along with sec=krb5 to search for\nprincipals from keytab is supported by cifs.upcall(8) since\ncifs-utils-4.8.  So fix this by matching username mount option in\nmatch_session() even with Kerberos.\n\nFor example, the second mount below should fail with -ENOKEY as there\nis no 'foobar' principal in keytab (/etc/krb5.keytab).  The client\nends up reusing SMB session from first mount to perform the second\none, which is wrong.\n\n```\n$ ktutil\nktutil:  add_entry -password -p testuser -k 1 -e aes256-cts\nPassword for [email protected]:\nktutil:  write_kt /etc/krb5.keytab\nktutil:  quit\n$ klist -ke\nKeytab name: FILE:/etc/krb5.keytab\nKVNO Principal\n ---- ----------------------------------------------------------------\n   1 [email protected] (aes256-cts-hmac-sha1-96)\n$ mount.cifs //w22-root2/scratch /mnt/1 -o sec=krb5,username=testuser\n$ mount.cifs //w22-root2/scratch /mnt/2 -o sec=krb5,username=foobar\n$ mount -t cifs | grep -Po 'username=\\K\\w+'\ntestuser\ntestuser\n```",
    "published": "2026-04-03T15:15:57.491Z",
    "modified": "2026-04-27T14:02:42.852Z",
    "type": "cve",
    "title": "smb: client: fix krb5 mount with username option",
    "source": "Linux",
    "references": "https://git.kernel.org/stable/c/fd4547830720647d4af02ee50f883c4b1cca06e4\nhttps://git.kernel.org/stable/c/9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2\nhttps://git.kernel.org/stable/c/d33cbf0bf8979d779900da9be2505d68d9d8da25\nhttps://git.kernel.org/stable/c/9ee803bfdba0cf739038dbdabdd4c02582c8f2b2\nhttps://git.kernel.org/stable/c/6e9ff1eb7feedcf46ff2d0503759960ab58e7775\nhttps://git.kernel.org/stable/c/12b4c5d98cd7ca46d5035a57bcd995df614c14e1",
    "id": "CVE-2026-31392",
    "bulletinFamily": "",
    "cwe": null,
    "cvelist": null,
    "sourceData": "Linux Linux 4ff67b720c02c36e54d55b88c2931879b7db1cd2\nLinux Linux 4ff67b720c02c36e54d55b88c2931879b7db1cd2\nLinux Linux 4ff67b720c02c36e54d55b88c2931879b7db1cd2\nLinux Linux 4ff67b720c02c36e54d55b88c2931879b7db1cd2\nLinux Linux 4ff67b720c02c36e54d55b88c2931879b7db1cd2\nLinux Linux 4ff67b720c02c36e54d55b88c2931879b7db1cd2\nLinux Linux 223c7f082d2836ac719b3b228bdcfab35e5e5330\nLinux Linux 88720224330a655ab6268e20109b65b11cfd7f6a\nLinux Linux 2.6.36",
    "sourceHref": "",
    "cvss": {
        "score": 8.1,
        "severity": "HIGH",
        "vector": "CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:L",
        "version": "3.1"
    },
    "cvss2": [],
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        "baseScore": 0,
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        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
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    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "Linux",
    "version": "4ff67b720c02c36e54d55b88c2931879b7db1cd2",
    "vendor": "Linux",
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    "ai_score": 0
}