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smb: server: fix active_num_conn leak on transport allocation failure

Type: advisorySource: Official CVE List1 source record

In the Linux kernel, the following vulnerability has been resolved: smb: server: fix active_num_conn leak on transport allocation failure Commit 77ffbcac4e56 ("smb: server: fix leak of active_num_conn in ksmbd_tcp_new_connection()") addressed the kthread_run() failure path. The earlier alloc_transport() == NULL path in the same function has the same leak, is reachable pre-authentication via any TCP connect to port 445, and was empirically reproduced on UML (ARCH=um, v7.0-rc7): a small number of forced allocation failures were sufficient to put ksmbd into a state where every subsequent connection attempt was rejected for the remainder of the boot. ksmbd_kthread_fn() increments active_num_conn before calling ksmbd_tcp_new_connection() and discards the return value, so when alloc_transport() returns NULL the socket is released and -ENOMEM returned without decrementing the counter. Each such failure permanently consumes one slot from the max_connections pool; once cumulative failures reach the cap, atomic_inc_return() hits the threshold on every subsequent accept and every new connection is rejected. The counter is only reset by module reload. An unauthenticated remote attacker can drive the server toward the memory pressure that makes alloc_transport() fail by holding open connections with large RFC1002 lengths up to MAX_STREAM_PROT_LEN (0x00FFFFFF); natural transient allocation failures on a loaded host produce the same drift more slowly. Mirror the existing rollback pattern in

Announced Source revision 1
Original source ↗

CVE-2026-31711

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-31711

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
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Prerequisites
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Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "4210c3555db4b38bade92331b153e583261f05f9",
        "lessThan": "dc2e7d595d68cf1be1ba64e3d30ebf3266bf7242",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "d5d7847e57ac69fa99c18b363a34419bcdb5a281",
        "lessThan": "60734c8bc3b4aa0672e251f08dda81977e4b5387",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "0d0d4680db22eda1eea785c47bbf66a9b33a8b16",
        "lessThan": "97f8d2648ef4871e4cd335e2d769cb40054a6772",
        "versionType": "git"
      },
      {
        "status": "affected",
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        "lessThan": "295a9fc6789d1011c36ded9f0f2907bb34fa0de4",
        "versionType": "git"
      },
      {
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        "lessThan": "283027aa93380380a0994f35dde3ec95318f2654",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "0d0d4680db22eda1eea785c47bbf66a9b33a8b16",
        "lessThan": "fb48185bcd946d42de7017cf27f912f8ab26acf0",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "0d0d4680db22eda1eea785c47bbf66a9b33a8b16",
        "lessThan": "6551300dc452ac16a855a83dbd1e74899542d3b3",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "5.15.91",
        "lessThan": "5.15.210",
        "versionType": "semver"
      },
      {
        "status": "affected",
        "version": "6.1.9",
        "lessThan": "6.1.175",
        "versionType": "semver"
      }
    ],
    "programFiles": [
      "fs/smb/server/transport_tcp.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "6.2"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "6.2",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "5.15.210",
        "versionType": "semver",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.1.175",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.136",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.84",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.25",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "7.0.2",
        "versionType": "semver",
        "lessThanOrEqual": "7.0.*"
      },
      {
        "status": "unaffected",
        "version": "7.1",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "fs/smb/server/transport_tcp.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-31711

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#28318 · Revision 1
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Publisher date
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