CVE-2026-93787 (GCVE-0-2026-93787)

Vulnerability from cvelistv5 – Published: 2026-09-24 16:02 – Updated: 2026-09-25 12:42
VLAI
Title
smb: client: bound dirent name against end of SMB response in cifs_filldir
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: bound dirent name against end of SMB response in cifs_filldir cifs_filldir() copies the entry name out of an SMB1 TRANS2_FIND_FIRST / FIND_NEXT response using a length (de.namelen) supplied by the server. The kmalloc'd SMB response buffer is bounded, but nothing checks that de.name + de.namelen still lies inside that buffer before the eventual filldir64() -> verify_dirent_name() -> memchr() reads namelen bytes. A hostile SMB1 server that returns an oversized FileNameLength in a directory entry therefore causes memchr() to read past the end of the response slab buffer. Reachable from any user who can list a directory on a CIFS mount served by an attacker-controlled server (getdents64() on the mounted directory): BUG: KASAN: slab-out-of-bounds in memchr+0x71/0x80 Read of size 1 at addr ffff88800e0640cc by task poc/115 Call Trace: dump_stack_lvl+0x64/0x80 print_report+0xce/0x620 kasan_report+0xec/0x120 memchr+0x71/0x80 filldir64+0x4c/0x6a0 cifs_filldir.constprop.0+0x9bb/0x1e00 cifs_readdir+0x2101/0x3380 iterate_dir+0x19c/0x520 __x64_sys_getdents64+0x126/0x210 do_syscall_64+0x107/0x5a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f Pass the end-of-response pointer down to cifs_filldir() and reject entries whose name would extend past that boundary. This bug was discovered by Artiphishell's vTriage pipeline, which generated a userspace reproducer (an emulated hostile SMB1 server plus a getdents64() client) that reliably triggers the KASAN report on an unpatched kernel. The fix below was drafted with the Claude coding assistant; a userspace reproducer is available on request.
Severity
8.1 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 6e3b965267b7313903baba2739992b1e2e92d540 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 03003506c86f90312b0966283662c42fcab66e4b (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < f8cf09a53a0dc1da298e9dd0ba5f21710cf119d6 (git)
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Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 6.12.111 , ≤ 6.12.* (semver)
Unaffected: 6.18.53 , ≤ 6.18.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
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    "cna": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/readdir.c"
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          "vendor": "Linux",
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              "versionType": "semver"
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              "version": "6.18.53",
              "versionType": "semver"
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              "status": "unaffected",
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              "versionType": "original_commit_for_fix"
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      "cpeApplicability": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.111",
                  "versionStartIncluding": "2.6.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                }
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              "negate": false,
              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: bound dirent name against end of SMB response in cifs_filldir\n\ncifs_filldir() copies the entry name out of an SMB1 TRANS2_FIND_FIRST /\nFIND_NEXT response using a length (de.namelen) supplied by the server.\nThe kmalloc\u0027d SMB response buffer is bounded, but nothing checks that\nde.name + de.namelen still lies inside that buffer before the eventual\nfilldir64() -\u003e verify_dirent_name() -\u003e memchr() reads namelen bytes.\n\nA hostile SMB1 server that returns an oversized FileNameLength in a\ndirectory entry therefore causes memchr() to read past the end of the\nresponse slab buffer. Reachable from any user who can list a directory\non a CIFS mount served by an attacker-controlled server (getdents64()\non the mounted directory):\n\n  BUG: KASAN: slab-out-of-bounds in memchr+0x71/0x80\n  Read of size 1 at addr ffff88800e0640cc by task poc/115\n  Call Trace:\n   dump_stack_lvl+0x64/0x80\n   print_report+0xce/0x620\n   kasan_report+0xec/0x120\n   memchr+0x71/0x80\n   filldir64+0x4c/0x6a0\n   cifs_filldir.constprop.0+0x9bb/0x1e00\n   cifs_readdir+0x2101/0x3380\n   iterate_dir+0x19c/0x520\n   __x64_sys_getdents64+0x126/0x210\n   do_syscall_64+0x107/0x5a0\n   entry_SYSCALL_64_after_hwframe+0x77/0x7f\n\nPass the end-of-response pointer down to cifs_filldir() and reject\nentries whose name would extend past that boundary.\n\nThis bug was discovered by Artiphishell\u0027s vTriage pipeline, which\ngenerated a userspace reproducer (an emulated hostile SMB1 server plus\na getdents64() client) that reliably triggers the KASAN report on an\nunpatched kernel. The fix below was drafted with the Claude coding\nassistant; a userspace reproducer is available on request."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - cifs_filldir() takes FileNameLength from an SMB1 TRANS2_FIND_FIRST/FIND_NEXT directory entry received over TCP/445; CIFSFindFirst() stores that PDU in srch_inf.ntwrk_buf_start and getdents64\u2192iterate_dir\u2192cifs_readdir() passes each entry to cifs_filldir(), so the oversized name length is protocol data from the remote SMB peer.\nAC:L - The hostile SMB1 server sets FileNameLength (cifs_fill_dirent_dir/full/search/both) and Flags2 unicode and can place FileName near the end of the CIFSFindFirst buffer so de.name+de.namelen exceeds end_of_smb; the old namelen\u003emax_len check only compared against the whole SMB size, so the overread is deterministic with no race.\nPR:N - The attacker is the remote SMB1 server (or a MITM on an unsigned SMB1 session) that returns the FIND_FIRST/FIND_NEXT payload; CIFSFindFirst() and cifs_filldir() use the victim\u0027s existing tcon and impose no account or capability check on that peer.\nUI:R - cifs_filldir() is reached only from cifs_dir_ops.iterate_shared (cifs_readdir) on getdents64\u2192iterate_dir; the SMB1 server cannot inject an unsolicited FIND response into that path, so a victim process must list a directory on the CIFS mount.\nS:U - The slab-out-of-bounds read in filldir64\u0027s verify_dirent_name()/memchr() stays inside the client kernel\u0027s CIFS response buffer on the same host; this is not a VM escape, IOMMU bypass, or sandbox boundary crossing.\nC:H - FileNameLength can be just under PATH_MAX while de.name sits at the end of the kmalloc\u0027d FIND response, so memchr() and filldir64\u0027s unsafe_copy_dirent_name() read up to ~4095 bytes of adjacent kernel heap and copy them into the getdents64 userspace buffer.\nI:N - The defect is an over-read of the FIND entry name; cifs_filldir() does not write past the SMB buffer, and filldir64 only copies the over-read bytes to the caller\u0027s dirent buffer, giving no kernel write or control-flow primitive.\nA:H - KASAN reports a slab-out-of-bounds read in memchr() from filldir64\u2190cifs_filldir on the hostile FileNameLength; walking those bytes off the cifs_request object into an unmapped page oopses or panics the client, and the server can retrigger it on every getdents64."
            }
          ]
        }
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      "providerMetadata": {
        "dateUpdated": "2026-09-25T12:42:52.958Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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          "url": "https://git.kernel.org/stable/c/6e3b965267b7313903baba2739992b1e2e92d540"
        },
        {
          "url": "https://git.kernel.org/stable/c/03003506c86f90312b0966283662c42fcab66e4b"
        },
        {
          "url": "https://git.kernel.org/stable/c/f8cf09a53a0dc1da298e9dd0ba5f21710cf119d6"
        }
      ],
      "title": "smb: client: bound dirent name against end of SMB response in cifs_filldir",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-93787",
    "datePublished": "2026-09-24T16:02:20.872Z",
    "dateReserved": "2026-09-18T17:59:28.788Z",
    "dateUpdated": "2026-09-25T12:42:52.958Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
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      "date": "2026-09-28",
      "epss": "0.00333",
      "percentile": "0.2398"
    },
    "microsoft_vex": {
      "current_release_date": "2026-09-28T01:21:14.000Z",
      "cve": "CVE-2026-93787",
      "id": "msrc_CVE-2026-93787",
      "initial_release_date": "2026-09-27T23:50:45.000Z",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "smb: client: bound dirent name against end of SMB response in cifs_filldir",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-93787.json",
      "version": "2"
    },
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                "product": "Linux",
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                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "version": "2.6.12"
                  },
                  {
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                  {
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                    "status": "unaffected",
                    "version": "6.12.111",
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                    "status": "unaffected",
                    "version": "6.18.53",
                    "versionType": "semver"
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            ],
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          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: bound dirent name against end of SMB response in cifs_filldir\n\ncifs_filldir() copies the entry name out of an SMB1 TRANS2_FIND_FIRST /\nFIND_NEXT response using a length (de.namelen) supplied by the server.\nThe kmalloc\u0027d SMB response buffer is bounded, but nothing checks that\nde.name + de.namelen still lies inside that buffer before the eventual\nfilldir64() -\u003e verify_dirent_name() -\u003e memchr() reads namelen bytes.\n\nA hostile SMB1 server that returns an oversized FileNameLength in a\ndirectory entry therefore causes memchr() to read past the end of the\nresponse slab buffer. Reachable from any user who can list a directory\non a CIFS mount served by an attacker-controlled server (getdents64()\non the mounted directory):\n\n  BUG: KASAN: slab-out-of-bounds in memchr+0x71/0x80\n  Read of size 1 at addr ffff88800e0640cc by task poc/115\n  Call Trace:\n   dump_stack_lvl+0x64/0x80\n   print_report+0xce/0x620\n   kasan_report+0xec/0x120\n   memchr+0x71/0x80\n   filldir64+0x4c/0x6a0\n   cifs_filldir.constprop.0+0x9bb/0x1e00\n   cifs_readdir+0x2101/0x3380\n   iterate_dir+0x19c/0x520\n   __x64_sys_getdents64+0x126/0x210\n   do_syscall_64+0x107/0x5a0\n   entry_SYSCALL_64_after_hwframe+0x77/0x7f\n\nPass the end-of-response pointer down to cifs_filldir() and reject\nentries whose name would extend past that boundary.\n\nThis bug was discovered by Artiphishell\u0027s vTriage pipeline, which\ngenerated a userspace reproducer (an emulated hostile SMB1 server plus\na getdents64() client) that reliably triggers the KASAN report on an\nunpatched kernel. The fix below was drafted with the Claude coding\nassistant; a userspace reproducer is available on request."
          }
        ],
        "id": "CVE-2026-93787",
        "lastModified": "2026-09-25T13:17:19.270",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 8.1,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "REQUIRED",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H",
                "version": "3.1"
              },
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              "impactScore": 5.2,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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        "published": "2026-09-24T17:17:11.363",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/03003506c86f90312b0966283662c42fcab66e4b"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/6e3b965267b7313903baba2739992b1e2e92d540"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/f8cf09a53a0dc1da298e9dd0ba5f21710cf119d6"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-09-28T10:35:45+00:00",
      "cve": "CVE-2026-93787",
      "id": "CVE-2026-93787",
      "initial_release_date": "2026-09-24T00:00:00+00:00",
      "product_status:known_affected": "234",
      "product_status:known_not_affected": "42",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: smb: client: bound dirent name against end of SMB response in cifs_filldir",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-93787.json",
      "version": "3"
    }
  }
}



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