CVE-2026-31392 (GCVE-0-2026-31392)
Vulnerability from cvelistv5
Published
2026-04-03 15:15
Modified
2026-04-27 14:02
Severity ?
8.1 (High) - CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:L
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: fix krb5 mount with username option Customer reported that some of their krb5 mounts were failing against a single server as the client was trying to mount the shares with wrong credentials. It turned out the client was reusing SMB session from first mount to try mounting the other shares, even though a different username= option had been specified to the other mounts. By using username mount option along with sec=krb5 to search for principals from keytab is supported by cifs.upcall(8) since cifs-utils-4.8. So fix this by matching username mount option in match_session() even with Kerberos. For example, the second mount below should fail with -ENOKEY as there is no 'foobar' principal in keytab (/etc/krb5.keytab). The client ends up reusing SMB session from first mount to perform the second one, which is wrong. ``` $ ktutil ktutil: add_entry -password -p testuser -k 1 -e aes256-cts Password for testuser@ZELDA.TEST: ktutil: write_kt /etc/krb5.keytab ktutil: quit $ klist -ke Keytab name: FILE:/etc/krb5.keytab KVNO Principal ---- ---------------------------------------------------------------- 1 testuser@ZELDA.TEST (aes256-cts-hmac-sha1-96) $ mount.cifs //w22-root2/scratch /mnt/1 -o sec=krb5,username=testuser $ mount.cifs //w22-root2/scratch /mnt/2 -o sec=krb5,username=foobar $ mount -t cifs | grep -Po 'username=\K\w+' testuser testuser ```
References
Impacted products
Vendor Product Version
Linux Linux Version: 4ff67b720c02c36e54d55b88c2931879b7db1cd2
Version: 4ff67b720c02c36e54d55b88c2931879b7db1cd2
Version: 4ff67b720c02c36e54d55b88c2931879b7db1cd2
Version: 4ff67b720c02c36e54d55b88c2931879b7db1cd2
Version: 4ff67b720c02c36e54d55b88c2931879b7db1cd2
Version: 4ff67b720c02c36e54d55b88c2931879b7db1cd2
Version: 223c7f082d2836ac719b3b228bdcfab35e5e5330
Version: 88720224330a655ab6268e20109b65b11cfd7f6a
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{
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          "programFiles": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "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 \u0027foobar\u0027 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 testuser@ZELDA.TEST:\nktutil:  write_kt /etc/krb5.keytab\nktutil:  quit\n$ klist -ke\nKeytab name: FILE:/etc/krb5.keytab\nKVNO Principal\n ---- ----------------------------------------------------------------\n   1 testuser@ZELDA.TEST (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 \u0027username=\\K\\w+\u0027\ntestuser\ntestuser\n```"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:L",
            "version": "3.1"
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      "providerMetadata": {
        "dateUpdated": "2026-04-27T14:02:42.852Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/fd4547830720647d4af02ee50f883c4b1cca06e4"
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        {
          "url": "https://git.kernel.org/stable/c/9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2"
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        },
        {
          "url": "https://git.kernel.org/stable/c/12b4c5d98cd7ca46d5035a57bcd995df614c14e1"
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      ],
      "title": "smb: client: fix krb5 mount with username option",
      "x_generator": {
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-31392",
    "datePublished": "2026-04-03T15:15:57.491Z",
    "dateReserved": "2026-03-09T15:48:24.085Z",
    "dateUpdated": "2026-04-27T14:02:42.852Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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