CVE-2026-89787 (GCVE-0-2026-89787)
Vulnerability from cvelistv5
Published
2026-09-16 08:48
Modified
2026-10-19 08:52
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: ext4: check dir entry fits before reading the hash trailer in ext4_search_dir() For casefolded encrypted directories ext4 stores an 8-byte hash trailer after the name (EXT4_DIRENT_HASHES()), at an offset derived from de->name_len. On the sb_no_casefold_compat_fallback() path ext4_match() reads that trailer, but ext4_search_dir()'s by-hand pre-check only tests de->name + de->name_len <= dlimit, which proves the name fits, not the rounded trailer. A crafted entry whose name ends at the block boundary passes the check while EXT4_DIRENT_HASHES(de) lands past the block end, so ext4_match() reads out of bounds on an ordinary lookup. KASAN reports it as a use-after-free when the page after the directory block holds a freed object: BUG: KASAN: use-after-free in ext4_match (fs/ext4/namei.c:1435) Read of size 4 at addr ffff888010458000 by task exploit Call Trace: ext4_match (fs/ext4/namei.c:1435) ext4_search_dir (fs/ext4/namei.c:1470) __ext4_find_entry (fs/ext4/namei.c:1268 fs/ext4/namei.c:1632) ext4_lookup (fs/ext4/namei.c:1703 fs/ext4/namei.c:1769) ... filename_lookup (fs/namei.c:2842) vfs_statx (fs/stat.c:353) __do_sys_newfstatat (fs/stat.c:538) do_syscall_64 (arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) Require, for hash-in-dirent directories, that the whole entry including the rounded trailer fits before calling ext4_match(). This is the same bound ext4_check_dir_entry() already enforces via ext4_dir_rec_len(), so no well-formed entry is rejected. The other caller, ext4_find_dest_de(), runs ext4_check_dir_entry() first and is unaffected.
References
Impacted products
Vendor Product Version
Linux Linux Version: 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500
Version: 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500
Version: 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500
Version: 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500
Version: 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500
Version: 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500
Version: 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/ext4/namei.c"
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        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/ext4/namei.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "5.13"
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              "version": "0",
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              "status": "unaffected",
              "version": "5.15.221",
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            },
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              "status": "unaffected",
              "version": "6.1.188",
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            },
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              "status": "unaffected",
              "version": "6.6.157",
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            },
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              "status": "unaffected",
              "version": "6.12.110",
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            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.52",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: check dir entry fits before reading the hash trailer in ext4_search_dir()\n\nFor casefolded encrypted directories ext4 stores an 8-byte hash trailer\nafter the name (EXT4_DIRENT_HASHES()), at an offset derived from\nde-\u003ename_len.  On the sb_no_casefold_compat_fallback() path ext4_match()\nreads that trailer, but ext4_search_dir()\u0027s by-hand pre-check only tests\nde-\u003ename + de-\u003ename_len \u003c= dlimit, which proves the name fits, not the\nrounded trailer.  A crafted entry whose name ends at the block boundary\npasses the check while EXT4_DIRENT_HASHES(de) lands past the block end,\nso ext4_match() reads out of bounds on an ordinary lookup.  KASAN reports\nit as a use-after-free when the page after the directory block holds a\nfreed object:\n\n  BUG: KASAN: use-after-free in ext4_match (fs/ext4/namei.c:1435)\n  Read of size 4 at addr ffff888010458000 by task exploit\n  Call Trace:\n   ext4_match (fs/ext4/namei.c:1435)\n   ext4_search_dir (fs/ext4/namei.c:1470)\n   __ext4_find_entry (fs/ext4/namei.c:1268 fs/ext4/namei.c:1632)\n   ext4_lookup (fs/ext4/namei.c:1703 fs/ext4/namei.c:1769)\n   ...\n   filename_lookup (fs/namei.c:2842)\n   vfs_statx (fs/stat.c:353)\n   __do_sys_newfstatat (fs/stat.c:538)\n   do_syscall_64 (arch/x86/entry/syscall_64.c:94)\n   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)\n\nRequire, for hash-in-dirent directories, that the whole entry including\nthe rounded trailer fits before calling ext4_match().  This is the same\nbound ext4_check_dir_entry() already enforces via ext4_dir_rec_len(), so\nno well-formed entry is rejected.  The other caller, ext4_find_dest_de(),\nruns ext4_check_dir_entry() first and is unaffected."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:52:40.961Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/4d20106c536b73c4a8a02652dc85e35898baebf7"
        },
        {
          "url": "https://git.kernel.org/stable/c/61a395967de06edba58760e81907a272db749faa"
        },
        {
          "url": "https://git.kernel.org/stable/c/e94676a08af6312aa72d8a981232b281f9bcfcf5"
        },
        {
          "url": "https://git.kernel.org/stable/c/d8c184bec24b5a00ae96d704856d935eaded1685"
        },
        {
          "url": "https://git.kernel.org/stable/c/3933884bc3102898b458c53fbd1ac52eb9cdb8a4"
        },
        {
          "url": "https://git.kernel.org/stable/c/83663c0b739480c00cfe785675db87520ec484ed"
        },
        {
          "url": "https://git.kernel.org/stable/c/c7e6b863d298f56522d0d08554bbea7f142e6588"
        }
      ],
      "title": "ext4: check dir entry fits before reading the hash trailer in ext4_search_dir()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89787",
    "datePublished": "2026-09-16T08:48:24.403Z",
    "dateReserved": "2026-09-11T19:38:34.766Z",
    "dateUpdated": "2026-10-19T08:52:40.961Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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