CVE-2026-64400 (GCVE-0-2026-64400)

Vulnerability from cvelistv5 – Published: 2026-07-25 08:50 – Updated: 2026-08-05 12:41
VLAI
Title
ksmbd: prevent path traversal bypass by restricting caseless retry
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: prevent path traversal bypass by restricting caseless retry ksmbd_vfs_path_lookup() enforces LOOKUP_BENEATH to restrict path resolution within the share root. When a crafted path attempts to escape the share boundary using parent-directory components ('..'), vfs_path_parent_lookup() detects this and immediately fails, returning -EXDEV. However, a bug exists in __ksmbd_vfs_kern_path() under caseless mode. The function fails to intercept the -EXDEV error and erroneously falls through to the caseless retry logic, which is intended only for genuinely missing files. During this retry process, the path is reconstructed, leading to an unintended LOOKUP_BENEATH bypass that allows write-capable users to create zero-length files or directories outside the exported share. Fix this by ensuring that the execution only proceeds to the caseless lookup retry when the error is specifically -ENOENT. Any other errors, such as -EXDEV from a path traversal attempt, must be returned immediately.
Severity
8.6 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 74d7970febf7e9005375aeda0df821d2edffc9f7 , < 8c9a4f1327eb71efbf14842e7b8a6d965077eb67 (git)
Affected: 74d7970febf7e9005375aeda0df821d2edffc9f7 , < 54bab9ba5a9f156ffa9324fcbe5a356fd0242f95 (git)
Affected: 019aae488dbc67c97a33db03652e20e2c9e3afa7 (git)
Affected: 6927ffe7479c72e7ebf885507227266a75f7c97d (git)
Affected: ef6cc1c465786b3e4e735d1ab8b616b3e94402df (git)
Affected: 5.15.145 , < 5.16 (semver)
Affected: 6.1.71 , < 6.2 (semver)
Affected: 6.3.10 , < 6.4 (semver)
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Linux Linux Affected: 6.4
Unaffected: 0 , < 6.4 (semver)
Unaffected: 7.1.4 , ≤ 7.1.* (semver)
Unaffected: 7.2-rc1 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
            "fs/smb/server/vfs.c"
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: prevent path traversal bypass by restricting caseless retry\n\nksmbd_vfs_path_lookup() enforces LOOKUP_BENEATH to restrict path\nresolution within the share root. When a crafted path attempts to\nescape the share boundary using parent-directory components (\u0027..\u0027),\nvfs_path_parent_lookup() detects this and immediately fails,\nreturning -EXDEV.\n\nHowever, a bug exists in __ksmbd_vfs_kern_path() under caseless mode.\nThe function fails to intercept the -EXDEV error and erroneously\nfalls through to the caseless retry logic, which is intended only\nfor genuinely missing files. During this retry process, the path\nis reconstructed, leading to an unintended LOOKUP_BENEATH bypass\nthat allows write-capable users to create zero-length files or\ndirectories outside the exported share.\n\nFix this by ensuring that the execution only proceeds to the caseless\nlookup retry when the error is specifically -ENOENT. Any other errors,\nsuch as -EXDEV from a path traversal attempt, must be returned immediately."
        }
      ],
      "metrics": [
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H",
            "version": "3.1"
          },
          "scenarios": [
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              "lang": "en",
              "value": "AV:N - The vulnerable lookup is reached remotely through SMB2 CREATE requests handled by ksmbd over TCP/445.\nAC:L - The attacker controls the crafted parent-directory path and can issue repeated or concurrent requests; any required lookup/create race is attacker-driven.\nPR:N - Although a valid SMB session and writable tree connection are required, ksmbd supports anonymous guest sessions on writable shares, requiring no prior privileges in a reasonable deployment.\nUI:N - Exploitation requires only attacker-generated SMB requests and no action by a victim.\nS:U - The bypass affects filesystems managed by the same host kernel and does not cross a virtualization or comparable security authority boundary.\nC:L - File contents are not exposed, but the out-of-share caseless directory walk and distinguishable errors can disclose limited pathname-existence metadata.\nI:L - The attacker can create chosen zero-length files or directories outside the export, but cannot supply file contents or overwrite arbitrary existing data through this flaw.\nA:H - Repeated creation in an escaped world-writable location can exhaust root-filesystem inodes, storage, or tmpfs memory and cause system-wide service unavailability."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:41:38.366Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/8c9a4f1327eb71efbf14842e7b8a6d965077eb67"
        },
        {
          "url": "https://git.kernel.org/stable/c/54bab9ba5a9f156ffa9324fcbe5a356fd0242f95"
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      "title": "ksmbd: prevent path traversal bypass by restricting caseless retry",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64400",
    "datePublished": "2026-07-25T08:50:43.655Z",
    "dateReserved": "2026-07-19T15:36:31.785Z",
    "dateUpdated": "2026-08-05T12:41:38.366Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "percentile": "0.2842"
    },
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      "cve": "CVE-2026-64400",
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      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
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      "title": "ksmbd: prevent path traversal bypass by restricting caseless retry",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-64400.json",
      "version": "2"
    },
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    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-07-29T11:14:53+00:00",
      "cve": "CVE-2026-64400",
      "id": "CVE-2026-64400",
      "initial_release_date": "2026-07-25T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ksmbd: prevent path traversal bypass by restricting caseless retry",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64400.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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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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