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CVE-2026-89636 (GCVE-0-2026-89636)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-14 12:01
VLAI
Title
smb: client: clear ce->tgthint in free_tgts()
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: clear ce->tgthint in free_tgts() When free_tgts() frees all structures in ce->tlist, ce->tgthint is left pointing to one of the freed cache_dfs_tgt structures. If ce->tgthint is not reset before it is used later, it results in a use-after-free. Set ce->tgthint to NULL in free_tgts() after the elements are freed to reflect that no elements remain.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 54be1f6c1c37498bba557049df646cc239fa37e3 , < 14f60e959b5ac813715ff72e127beb3584ddabf6 (git)
Affected: 54be1f6c1c37498bba557049df646cc239fa37e3 , < 3ff9462bb7a06d8d32a1dc02d39580b078ec9e55 (git)
Affected: 54be1f6c1c37498bba557049df646cc239fa37e3 , < 7507bd1885643d0461a6017767492450af1ce2a3 (git)
Affected: 54be1f6c1c37498bba557049df646cc239fa37e3 , < 9ab46a13798a61d9d020b01d4e57efdabe6624fa (git)
Affected: 54be1f6c1c37498bba557049df646cc239fa37e3 , < 5baab40404a9393bcc0b7b8f1950bf2c307e0984 (git)
Affected: 54be1f6c1c37498bba557049df646cc239fa37e3 , < b1b741cf8e7ce1b91d937e23decd3d3358748700 (git)
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Linux Linux Affected: 5.0
Unaffected: 0 , < 5.0 (semver)
Unaffected: 6.1.188 , ≤ 6.1.* (semver)
Unaffected: 6.6.157 , ≤ 6.6.* (semver)
Unaffected: 6.12.109 , ≤ 6.12.* (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/dfs_cache.c"
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              "version": "0",
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              "version": "6.1.188",
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              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.12.109",
              "versionType": "semver"
            },
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              "status": "unaffected",
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              "versionType": "semver"
            },
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              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
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              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
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        }
      ],
      "cpeApplicability": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "5.0",
                  "vulnerable": true
                },
                {
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                  "versionEndExcluding": "6.6.157",
                  "versionStartIncluding": "5.0",
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: clear ce-\u003etgthint in free_tgts()\n\nWhen free_tgts() frees all structures in ce-\u003etlist, ce-\u003etgthint\nis left pointing to one of the freed cache_dfs_tgt structures.\n\nIf ce-\u003etgthint is not reset before it is used later, it results\nin a use-after-free.\n\nSet ce-\u003etgthint to NULL in free_tgts() after the elements are\nfreed to reflect that no elements remain."
        }
      ],
      "metrics": [
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            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
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              "value": "AV:N - The dangling ce-\u003etgthint is created while handling FSCTL_DFS_GET_REFERRALS/TRANS2_GET_DFS_REFERRAL replies from a remote SMB server over TCP/445 (smb2_get_dfs_refer \u2192 cache_refresh_path \u2192 update_cache_entry_locked \u2192 free_tgts). A malicious, compromised, or MITM\u0027d DFS server reaches this purely over the network.\nAC:L - A hostile DFS server controls referral TTL (down to CACHE_MIN_TTL), target lists, and TCP resets that drive dfs_cache_refresh and reconnect into update_cache_entry_locked; after free_tgts() the later get_tgt_name()/dfs_cache_noreq_update_tgthint() use is deterministic, and the attacker can size and retry referrals to leave the stale hint and reclaim the slab.\nPR:N - The attacker is the remote SMB/DFS peer (or a MITM on an unsigned session) and needs no account, capability, or local privileges on the victim; the client authenticates to that server, and the kernel DFS cache parses the reply regardless of which local user owns the mount.\nUI:N - Once a DFS CIFS mount exists (fstab, autofs/systemd automount, enterprise DFS, cifsroot), dfs_cache_refresh delayed work and reconnect-driven cifs_tree_connect()/dfs_cache_noreq_find() use the stale tgthint automatically after a server-induced refresh or TCP drop, with no further user action.\nS:U - The use-after-free is of kmalloc\u0027d cache_dfs_tgt objects in the client kernel heap and remains in the same host kernel security authority; it does not cross a VM, IOMMU, or sandbox boundary.\nC:H - get_tgt_name() and dfs_cache_noreq_update_tgthint() dereference the freed cache_dfs_tgt (t-\u003ename). Reclaiming that slab with attacker-controlled SMB allocations yields an arbitrary kernel read via kstrdup/strcasecmp of a sprayed name pointer.\nI:H - Use-after-free of the heap cache_dfs_tgt enables heap spraying and overlapping live objects; the dangling hint is also copied into DFS referral state and used for failover tree-connect, giving a write/control-flow primitive once the object is reclaimed.\nA:H - Dereferencing the freed cache_dfs_tgt from reconnect (cifs_tree_connect \u2192 dfs_cache_noreq_find) or dfs_cache_find oopses or panics the client kernel, and a malicious server can retrigger it on every refresh or reconnect."
            }
          ]
        }
      ],
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        "dateUpdated": "2026-09-14T12:01:41.762Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/14f60e959b5ac813715ff72e127beb3584ddabf6"
        },
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          "url": "https://git.kernel.org/stable/c/3ff9462bb7a06d8d32a1dc02d39580b078ec9e55"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89636",
    "datePublished": "2026-09-11T19:45:30.283Z",
    "dateReserved": "2026-09-11T19:38:34.739Z",
    "dateUpdated": "2026-09-14T12:01:41.762Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
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      "date": "2026-09-16",
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-13T06:50:59+00:00",
      "cve": "CVE-2026-89636",
      "id": "CVE-2026-89636",
      "initial_release_date": "2026-09-11T19:45:30.283000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel SMB client: Use-after-free vulnerability due to improper handling of freed structures",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89636.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "critical",
      "current_release_date": "2026-09-13T16:57:46Z",
      "cve": "CVE-2026-89636",
      "id": "CVE-2026-89636",
      "initial_release_date": "2026-09-12T16:24:35Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89636",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89636.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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