FKIE_CVE-2026-92499

Vulnerability from fkie_nvd - Published: 2026-09-17 17:17 - Updated: 2026-09-17 17:17
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: ext4: validate readdir offset before accessing dirent A corrupted directory can trigger the following KASAN report when ext4_readdir() resumes from an invalid position: BUG: KASAN: use-after-free in __ext4_check_dir_entry+0x5ef/0x820 Read of size 2 at addr ffff88810a646000 by task repro_linear/509 Call Trace: <TASK> dump_stack_lvl+0x53/0x70 print_report+0xd0/0x630 kasan_report+0xce/0x100 __ext4_check_dir_entry+0x5ef/0x820 ext4_readdir+0xcde/0x2b70 iterate_dir+0x1a1/0x520 __x64_sys_getdents64+0x12b/0x220 do_syscall_64+0xf9/0x540 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> KASAN reports use-after-free because the out-of-bounds access lands in an adjacent freed page. The directory buffer itself is still referenced. ext4_dir_llseek() invalidates the directory cookie so that ext4_readdir() rescans directory entries from the start of the block. The rescan checks only the lower bound of rec_len before advancing. A corrupted rec_len can therefore place the offset where the block has insufficient space for a complete directory entry. The rescan itself may dereference that truncated entry, or the main loop may pass it to __ext4_check_dir_entry(). The latter reads de->rec_len before validating the range. For example: block offset 0 4092 4096 |---- de1.rec_len = 4092 -----|----| de2.inode | de2.rec_len ^ OOB, reported as UAF de2 starts at offset 4092 in this 4 KiB block. Its four-byte inode fits in the block, but its rec_len starts at offset 4096 and crosses the boundary. The minimum safe length is inode-dependent. Encrypted and casefolded directory entries need eight additional hash bytes, while a valid metadata checksum tail is only 12 bytes. Cache the metadata checksum feature state and derive the minimum directory entry length from the on-disk format. Use it to bound both the rescan and the offset passed to the main loop. Report an offset in a truncated block tail and skip the remainder of the block, while continuing to accept an offset exactly at the block boundary.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/64d445d40e5ea4c4d4d88880db753b370cb69161
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b4c728577933753180e3e97f08424d5bcaff705e
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/bc4b7b0414c33b2c8898eb04386df0d21a13dad8
Impacted products
Vendor Product Version
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{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/ext4/dir.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "64d445d40e5ea4c4d4d88880db753b370cb69161",
              "status": "affected",
              "version": "ac27a0ec112a089f1a5102bc8dffc79c8c815571",
              "versionType": "git"
            },
            {
              "lessThan": "b4c728577933753180e3e97f08424d5bcaff705e",
              "status": "affected",
              "version": "ac27a0ec112a089f1a5102bc8dffc79c8c815571",
              "versionType": "git"
            },
            {
              "lessThan": "bc4b7b0414c33b2c8898eb04386df0d21a13dad8",
              "status": "affected",
              "version": "ac27a0ec112a089f1a5102bc8dffc79c8c815571",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/ext4/dir.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.19"
            },
            {
              "lessThan": "2.6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "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-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: validate readdir offset before accessing dirent\n\nA corrupted directory can trigger the following KASAN report when\next4_readdir() resumes from an invalid position:\n\n  BUG: KASAN: use-after-free in __ext4_check_dir_entry+0x5ef/0x820\n  Read of size 2 at addr ffff88810a646000 by task repro_linear/509\n\n  Call Trace:\n   \u003cTASK\u003e\n   dump_stack_lvl+0x53/0x70\n   print_report+0xd0/0x630\n   kasan_report+0xce/0x100\n   __ext4_check_dir_entry+0x5ef/0x820\n   ext4_readdir+0xcde/0x2b70\n   iterate_dir+0x1a1/0x520\n   __x64_sys_getdents64+0x12b/0x220\n   do_syscall_64+0xf9/0x540\n   entry_SYSCALL_64_after_hwframe+0x77/0x7f\n   \u003c/TASK\u003e\n\nKASAN reports use-after-free because the out-of-bounds access lands in an\nadjacent freed page. The directory buffer itself is still referenced.\n\next4_dir_llseek() invalidates the directory cookie so that ext4_readdir()\nrescans directory entries from the start of the block. The rescan checks\nonly the lower bound of rec_len before advancing. A corrupted rec_len can\ntherefore place the offset where the block has insufficient space for a\ncomplete directory entry. The rescan itself may dereference that truncated\nentry, or the main loop may pass it to __ext4_check_dir_entry(). The latter\nreads de-\u003erec_len before validating the range. For example:\n\n  block offset  0                           4092  4096\n                |---- de1.rec_len = 4092 -----|----|\n                                               de2.inode\n                                                    | de2.rec_len\n                                                    ^ OOB, reported as UAF\n\nde2 starts at offset 4092 in this 4 KiB block. Its four-byte inode fits in\nthe block, but its rec_len starts at offset 4096 and crosses the boundary.\n\nThe minimum safe length is inode-dependent. Encrypted and casefolded\ndirectory entries need eight additional hash bytes, while a valid metadata\nchecksum tail is only 12 bytes.\n\nCache the metadata checksum feature state and derive the minimum directory\nentry length from the on-disk format. Use it to bound both the rescan and\nthe offset passed to the main loop. Report an offset in a truncated block\ntail and skip the remainder of the block, while continuing to accept an\noffset exactly at the block boundary."
    }
  ],
  "id": "CVE-2026-92499",
  "lastModified": "2026-09-17T17:17:52.280",
  "metrics": {},
  "published": "2026-09-17T17:17:52.280",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/64d445d40e5ea4c4d4d88880db753b370cb69161"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b4c728577933753180e3e97f08424d5bcaff705e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/bc4b7b0414c33b2c8898eb04386df0d21a13dad8"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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