Vulnerability-Lookup

FKIE_CVE-2021-47656

Vulnerability from fkie_nvd - Published: 2025-02-26 06:37 - Updated: 2026-08-04 10:17

Severity

7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Summary

In the Linux kernel, the following vulnerability has been resolved: jffs2: fix use-after-free in jffs2_clear_xattr_subsystem When we mount a jffs2 image, assume that the first few blocks of the image are normal and contain at least one xattr-related inode, but the next block is abnormal. As a result, an error is returned in jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then called in jffs2_build_filesystem() and then again in jffs2_do_fill_super(). Finally we can observe the following report: ================================================================== BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem+0x95/0x6ac Read of size 8 at addr ffff8881243384e0 by task mount/719 Call Trace: dump_stack+0x115/0x16b jffs2_clear_xattr_subsystem+0x95/0x6ac jffs2_do_fill_super+0x84f/0xc30 jffs2_fill_super+0x2ea/0x4c0 mtd_get_sb+0x254/0x400 mtd_get_sb_by_nr+0x4f/0xd0 get_tree_mtd+0x498/0x840 jffs2_get_tree+0x25/0x30 vfs_get_tree+0x8d/0x2e0 path_mount+0x50f/0x1e50 do_mount+0x107/0x130 __se_sys_mount+0x1c5/0x2f0 __x64_sys_mount+0xc7/0x160 do_syscall_64+0x45/0x70 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Allocated by task 719: kasan_save_stack+0x23/0x60 __kasan_kmalloc.constprop.0+0x10b/0x120 kasan_slab_alloc+0x12/0x20 kmem_cache_alloc+0x1c0/0x870 jffs2_alloc_xattr_ref+0x2f/0xa0 jffs2_scan_medium.cold+0x3713/0x4794 jffs2_do_mount_fs.cold+0xa7/0x2253 jffs2_do_fill_super+0x383/0xc30 jffs2_fill_super+0x2ea/0x4c0 [...] Freed by task 719: kmem_cache_free+0xcc/0x7b0 jffs2_free_xattr_ref+0x78/0x98 jffs2_clear_xattr_subsystem+0xa1/0x6ac jffs2_do_mount_fs.cold+0x5e6/0x2253 jffs2_do_fill_super+0x383/0xc30 jffs2_fill_super+0x2ea/0x4c0 [...] The buggy address belongs to the object at ffff8881243384b8 which belongs to the cache jffs2_xattr_ref of size 48 The buggy address is located 40 bytes inside of 48-byte region [ffff8881243384b8, ffff8881243384e8) [...] ================================================================== The triggering of the BUG is shown in the following stack: ----------------------------------------------------------- jffs2_fill_super jffs2_do_fill_super jffs2_do_mount_fs jffs2_build_filesystem jffs2_scan_medium jffs2_scan_eraseblock <--- ERROR jffs2_clear_xattr_subsystem <--- free jffs2_clear_xattr_subsystem <--- free again ----------------------------------------------------------- An error is returned in jffs2_do_mount_fs(). If the error is returned by jffs2_sum_init(), the jffs2_clear_xattr_subsystem() does not need to be executed. If the error is returned by jffs2_build_filesystem(), the jffs2_clear_xattr_subsystem() also does not need to be executed again. So move jffs2_clear_xattr_subsystem() from 'out_inohash' to 'out_root' to fix this UAF problem.

References

URL	Tags
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/9150cb625b46f68d524f4cfd491f1aafc23e10a9	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101	Patch

Impacted products

Vendor	Product	Version
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*

JSON

To clipboard

{
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  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\njffs2: fix use-after-free in jffs2_clear_xattr_subsystem\n\nWhen we mount a jffs2 image, assume that the first few blocks of\nthe image are normal and contain at least one xattr-related inode,\nbut the next block is abnormal. As a result, an error is returned\nin jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then\ncalled in jffs2_build_filesystem() and then again in\njffs2_do_fill_super().\n\nFinally we can observe the following report:\n ==================================================================\n BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem+0x95/0x6ac\n Read of size 8 at addr ffff8881243384e0 by task mount/719\n\n Call Trace:\n  dump_stack+0x115/0x16b\n  jffs2_clear_xattr_subsystem+0x95/0x6ac\n  jffs2_do_fill_super+0x84f/0xc30\n  jffs2_fill_super+0x2ea/0x4c0\n  mtd_get_sb+0x254/0x400\n  mtd_get_sb_by_nr+0x4f/0xd0\n  get_tree_mtd+0x498/0x840\n  jffs2_get_tree+0x25/0x30\n  vfs_get_tree+0x8d/0x2e0\n  path_mount+0x50f/0x1e50\n  do_mount+0x107/0x130\n  __se_sys_mount+0x1c5/0x2f0\n  __x64_sys_mount+0xc7/0x160\n  do_syscall_64+0x45/0x70\n  entry_SYSCALL_64_after_hwframe+0x44/0xa9\n\n Allocated by task 719:\n  kasan_save_stack+0x23/0x60\n  __kasan_kmalloc.constprop.0+0x10b/0x120\n  kasan_slab_alloc+0x12/0x20\n  kmem_cache_alloc+0x1c0/0x870\n  jffs2_alloc_xattr_ref+0x2f/0xa0\n  jffs2_scan_medium.cold+0x3713/0x4794\n  jffs2_do_mount_fs.cold+0xa7/0x2253\n  jffs2_do_fill_super+0x383/0xc30\n  jffs2_fill_super+0x2ea/0x4c0\n [...]\n\n Freed by task 719:\n  kmem_cache_free+0xcc/0x7b0\n  jffs2_free_xattr_ref+0x78/0x98\n  jffs2_clear_xattr_subsystem+0xa1/0x6ac\n  jffs2_do_mount_fs.cold+0x5e6/0x2253\n  jffs2_do_fill_super+0x383/0xc30\n  jffs2_fill_super+0x2ea/0x4c0\n [...]\n\n The buggy address belongs to the object at ffff8881243384b8\n  which belongs to the cache jffs2_xattr_ref of size 48\n The buggy address is located 40 bytes inside of\n  48-byte region [ffff8881243384b8, ffff8881243384e8)\n [...]\n ==================================================================\n\nThe triggering of the BUG is shown in the following stack:\n-----------------------------------------------------------\njffs2_fill_super\n  jffs2_do_fill_super\n    jffs2_do_mount_fs\n      jffs2_build_filesystem\n        jffs2_scan_medium\n          jffs2_scan_eraseblock        \u003c--- ERROR\n        jffs2_clear_xattr_subsystem    \u003c--- free\n    jffs2_clear_xattr_subsystem        \u003c--- free again\n-----------------------------------------------------------\n\nAn error is returned in jffs2_do_mount_fs(). If the error is returned\nby jffs2_sum_init(), the jffs2_clear_xattr_subsystem() does not need to\nbe executed. If the error is returned by jffs2_build_filesystem(), the\njffs2_clear_xattr_subsystem() also does not need to be executed again.\nSo move jffs2_clear_xattr_subsystem() from \u0027out_inohash\u0027 to \u0027out_root\u0027\nto fix this UAF problem."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: jffs2: se corrige el use-after-free en jffs2_clear_xattr_subsystem Cuando montamos una imagen jffs2, asumimos que los primeros bloques de la imagen son normales y contienen al menos un inodo relacionado con xattr, pero el siguiente bloque es anormal. Como resultado, se devuelve un error en jffs2_scan_eraseblock(). Luego se llama a jffs2_clear_xattr_subsystem() en jffs2_build_filesystem() y luego nuevamente en jffs2_do_fill_super(). Finalmente podemos observar el siguiente reporte: ======================================================================= ERROR: KASAN: use-after-free en jffs2_clear_xattr_subsystem+0x95/0x6ac Lectura de tama\u00f1o 8 en la direcci\u00f3n ffff8881243384e0 por la tarea mount/719 Rastreo de llamadas: dump_stack+0x115/0x16b jffs2_clear_xattr_subsystem+0x95/0x6ac jffs2_do_fill_super+0x84f/0xc30 jffs2_fill_super+0x2ea/0x4c0 mtd_get_sb+0x254/0x400 mtd_get_sb_by_nr+0x4f/0xd0 get_tree_mtd+0x498/0x840 jffs2_get_tree+0x25/0x30 vfs_get_tree+0x8d/0x2e0 path_mount+0x50f/0x1e50 do_mount+0x107/0x130 __se_sys_mount+0x1c5/0x2f0 __x64_sys_mount+0xc7/0x160 do_syscall_64+0x45/0x70 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Asignado por la tarea 719: kasan_save_stack+0x23/0x60 __kasan_kmalloc.constprop.0+0x10b/0x120 kasan_slab_alloc+0x12/0x20 kmem_cache_alloc+0x1c0/0x870 jffs2_alloc_xattr_ref+0x2f/0xa0 jffs2_scan_medium.cold+0x3713/0x4794 jffs2_do_mount_fs.cold+0xa7/0x2253 jffs2_do_fill_super+0x383/0xc30 jffs2_fill_super+0x2ea/0x4c0 [...] Liberado por la tarea 719: kmem_cache_free+0xcc/0x7b0 jffs2_free_xattr_ref+0x78/0x98 jffs2_clear_xattr_subsystem+0xa1/0x6ac jffs2_do_mount_fs.cold+0x5e6/0x2253 jffs2_do_fill_super+0x383/0xc30 jffs2_fill_super+0x2ea/0x4c0 [...] La direcci\u00f3n con errores pertenece al objeto en ffff8881243384b8 que pertenece al cach\u00e9 jffs2_xattr_ref de tama\u00f1o 48 La direcci\u00f3n con errores se encuentra 40 bytes dentro de la regi\u00f3n de 48 bytes [ffff8881243384b8, ffff8881243384e8) [...] ========================================================================== La activaci\u00f3n del ERROR se muestra en la siguiente pila: ----------------------------------------------------------- jffs2_fill_super jffs2_do_fill_super jffs2_do_mount_fs jffs2_build_filesystem jffs2_scan_medium jffs2_scan_eraseblock \u0026lt;--- ERROR jffs2_clear_xattr_subsystem \u0026lt;--- free jffs2_clear_xattr_subsystem \u0026lt;--- free again ----------------------------------------------------------- Se devuelve un error en jffs2_do_mount_fs(). Si jffs2_sum_init() devuelve el error, no es necesario ejecutar jffs2_clear_xattr_subsystem(). Si jffs2_build_filesystem() devuelve el error, tampoco es necesario volver a ejecutar jffs2_clear_xattr_subsystem(). Por lo tanto, mueva jffs2_clear_xattr_subsystem() de \u0027out_inohash\u0027 a \u0027out_root\u0027 para solucionar este problema de UAF."
    }
  ],
  "id": "CVE-2021-47656",
  "lastModified": "2026-08-04T10:17:12.300",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.9,
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary"
      },
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.9,
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2021-47656",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2025-02-27T17:59:35.381270Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2025-02-26T06:37:07.360",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
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      "url": "https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
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      "url": "https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422"
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        "Patch"
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      "url": "https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/9150cb625b46f68d524f4cfd491f1aafc23e10a9"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-416"
        }
      ],
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "type": "Secondary"
    }
  ]
}

CVE-2021-47656 (GCVE-0-2021-47656)

Vulnerability from cvelistv5 – Published: 2025-02-26 01:54 – Updated: 2026-08-05 08:48

Title

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem

Summary

Severity

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2025-02-27 17:59 UTC

CWE

CWE-416 - Use After Free

Assigner

Linux mitre root

References

9 references

URL	Tags
https://git.kernel.org/stable/c/9150cb625b46f68d5…
https://git.kernel.org/stable/c/3bd2454162ec6bbb5…
https://git.kernel.org/stable/c/c3b07c875fa8f906f…
https://git.kernel.org/stable/c/30bf7244acf32f19c…
https://git.kernel.org/stable/c/7bb7428dd73991bf4…
https://git.kernel.org/stable/c/7a75740206af5f17e…
https://git.kernel.org/stable/c/22327bd7988f21de3…
https://git.kernel.org/stable/c/8c0f024f29e055840…
https://git.kernel.org/stable/c/4c7c44ee1650677fb…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: aa98d7cf59b5b0764d3502662053489585faf2fe , < 9150cb625b46f68d524f4cfd491f1aafc23e10a9 (git) Affected: aa98d7cf59b5b0764d3502662053489585faf2fe , < 3bd2454162ec6bbb5503233c804fce6e4b6dcec5 (git) Affected: aa98d7cf59b5b0764d3502662053489585faf2fe , < c3b07c875fa8f906f932976460fd14798596f101 (git) Affected: aa98d7cf59b5b0764d3502662053489585faf2fe , < 30bf7244acf32f19cb722c39f7bc1c2a9f300422 (git) Affected: aa98d7cf59b5b0764d3502662053489585faf2fe , < 7bb7428dd73991bf4b3a7a61b493ca50046c2b13 (git) Affected: aa98d7cf59b5b0764d3502662053489585faf2fe , < 7a75740206af5f17e9f3efa384211cba70213da1 (git) Affected: aa98d7cf59b5b0764d3502662053489585faf2fe , < 22327bd7988f21de3a53c1373f3b81542bfe1f44 (git) Affected: aa98d7cf59b5b0764d3502662053489585faf2fe , < 8c0f024f29e055840a5a89fe23b96ae3f921afed (git) Affected: aa98d7cf59b5b0764d3502662053489585faf2fe , < 4c7c44ee1650677fbe89d86edbad9497b7679b5c (git)
Linux	Linux	Affected: 2.6.18 Unaffected: 0 , < 2.6.18 (semver) Unaffected: 4.9.311 , ≤ 4.9.* (semver) Unaffected: 4.14.276 , ≤ 4.14.* (semver) Unaffected: 4.19.238 , ≤ 4.19.* (semver) Unaffected: 5.4.189 , ≤ 5.4.* (semver) Unaffected: 5.10.110 , ≤ 5.10.* (semver) Unaffected: 5.15.33 , ≤ 5.15.* (semver) Unaffected: 5.16.19 , ≤ 5.16.* (semver) Unaffected: 5.17.2 , ≤ 5.17.* (semver) Unaffected: 5.18 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "cvssV3_1": {
              "attackComplexity": "LOW",
              "attackVector": "LOCAL",
              "availabilityImpact": "HIGH",
              "baseScore": 7.8,
              "baseSeverity": "HIGH",
              "confidentialityImpact": "HIGH",
              "integrityImpact": "HIGH",
              "privilegesRequired": "LOW",
              "scope": "UNCHANGED",
              "userInteraction": "NONE",
              "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
              "version": "3.1"
            }
          },
          {
            "other": {
              "content": {
                "id": "CVE-2021-47656",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2025-02-27T17:59:35.381270Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "problemTypes": [
          {
            "descriptions": [
              {
                "cweId": "CWE-416",
                "description": "CWE-416 Use After Free",
                "lang": "en",
                "type": "CWE"
              }
            ]
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2025-02-27T18:02:30.510Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/jffs2/fs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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            {
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              "status": "affected",
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            {
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            {
              "lessThan": "7a75740206af5f17e9f3efa384211cba70213da1",
              "status": "affected",
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            {
              "lessThan": "22327bd7988f21de3a53c1373f3b81542bfe1f44",
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            {
              "lessThan": "8c0f024f29e055840a5a89fe23b96ae3f921afed",
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              "version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
              "versionType": "git"
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            {
              "lessThan": "4c7c44ee1650677fbe89d86edbad9497b7679b5c",
              "status": "affected",
              "version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/jffs2/fs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.18"
            },
            {
              "lessThan": "2.6.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "4.9.*",
              "status": "unaffected",
              "version": "4.9.311",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "4.14.*",
              "status": "unaffected",
              "version": "4.14.276",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "4.19.*",
              "status": "unaffected",
              "version": "4.19.238",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.4.*",
              "status": "unaffected",
              "version": "5.4.189",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.110",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.33",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.16.*",
              "status": "unaffected",
              "version": "5.16.19",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.17.*",
              "status": "unaffected",
              "version": "5.17.2",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "5.18",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "4.9.311",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "4.14.276",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "4.19.238",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.4.189",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.110",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.33",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.16.19",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.17.2",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.18",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\njffs2: fix use-after-free in jffs2_clear_xattr_subsystem\n\nWhen we mount a jffs2 image, assume that the first few blocks of\nthe image are normal and contain at least one xattr-related inode,\nbut the next block is abnormal. As a result, an error is returned\nin jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then\ncalled in jffs2_build_filesystem() and then again in\njffs2_do_fill_super().\n\nFinally we can observe the following report:\n ==================================================================\n BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem+0x95/0x6ac\n Read of size 8 at addr ffff8881243384e0 by task mount/719\n\n Call Trace:\n  dump_stack+0x115/0x16b\n  jffs2_clear_xattr_subsystem+0x95/0x6ac\n  jffs2_do_fill_super+0x84f/0xc30\n  jffs2_fill_super+0x2ea/0x4c0\n  mtd_get_sb+0x254/0x400\n  mtd_get_sb_by_nr+0x4f/0xd0\n  get_tree_mtd+0x498/0x840\n  jffs2_get_tree+0x25/0x30\n  vfs_get_tree+0x8d/0x2e0\n  path_mount+0x50f/0x1e50\n  do_mount+0x107/0x130\n  __se_sys_mount+0x1c5/0x2f0\n  __x64_sys_mount+0xc7/0x160\n  do_syscall_64+0x45/0x70\n  entry_SYSCALL_64_after_hwframe+0x44/0xa9\n\n Allocated by task 719:\n  kasan_save_stack+0x23/0x60\n  __kasan_kmalloc.constprop.0+0x10b/0x120\n  kasan_slab_alloc+0x12/0x20\n  kmem_cache_alloc+0x1c0/0x870\n  jffs2_alloc_xattr_ref+0x2f/0xa0\n  jffs2_scan_medium.cold+0x3713/0x4794\n  jffs2_do_mount_fs.cold+0xa7/0x2253\n  jffs2_do_fill_super+0x383/0xc30\n  jffs2_fill_super+0x2ea/0x4c0\n [...]\n\n Freed by task 719:\n  kmem_cache_free+0xcc/0x7b0\n  jffs2_free_xattr_ref+0x78/0x98\n  jffs2_clear_xattr_subsystem+0xa1/0x6ac\n  jffs2_do_mount_fs.cold+0x5e6/0x2253\n  jffs2_do_fill_super+0x383/0xc30\n  jffs2_fill_super+0x2ea/0x4c0\n [...]\n\n The buggy address belongs to the object at ffff8881243384b8\n  which belongs to the cache jffs2_xattr_ref of size 48\n The buggy address is located 40 bytes inside of\n  48-byte region [ffff8881243384b8, ffff8881243384e8)\n [...]\n ==================================================================\n\nThe triggering of the BUG is shown in the following stack:\n-----------------------------------------------------------\njffs2_fill_super\n  jffs2_do_fill_super\n    jffs2_do_mount_fs\n      jffs2_build_filesystem\n        jffs2_scan_medium\n          jffs2_scan_eraseblock        \u003c--- ERROR\n        jffs2_clear_xattr_subsystem    \u003c--- free\n    jffs2_clear_xattr_subsystem        \u003c--- free again\n-----------------------------------------------------------\n\nAn error is returned in jffs2_do_mount_fs(). If the error is returned\nby jffs2_sum_init(), the jffs2_clear_xattr_subsystem() does not need to\nbe executed. If the error is returned by jffs2_build_filesystem(), the\njffs2_clear_xattr_subsystem() also does not need to be executed again.\nSo move jffs2_clear_xattr_subsystem() from \u0027out_inohash\u0027 to \u0027out_root\u0027\nto fix this UAF problem."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is reached only through the local mount path (mount \u2192 jffs2_get_tree \u2192 get_tree_mtd \u2192 jffs2_fill_super \u2192 jffs2_do_fill_super \u2192 jffs2_do_mount_fs \u2192 jffs2_build_filesystem), parsing an MTD/JFFS2 image; there is no network-facing consumer.\nAC:L - An attacker who crafts the image fully controls the trigger\u2014place valid XREF/XATTR nodes in early eraseblocks so jffs2_alloc_xattr_ref() populates xref_temp, then make a later block fail jffs2_scan_eraseblock()\u2014with no race or attacker-uncontrollable condition.\nPR:N - The attacker needs no account on the target; they only supply the crafted JFFS2/MTD image (firmware blob, flash/SD contents), and CAP_SYS_ADMIN belongs to the victim or tooling that mounts it, matching the crafted-filesystem-image pattern.\nUI:R - Exploitation requires a victim (root, firmware updater, or automounter) to mount the attacker-supplied JFFS2 image so the failing scan hits the double clear_xattr path.\nS:U - The use-after-free corrupts kernel slab memory within the same host OS security authority; no VM escape, IOMMU bypass, or other cross-boundary compromise occurs.\nC:H - jffs2_clear_xattr_subsystem() frees xref_temp without NULLing it, so the second call reads ref-\u003enext from freed jffs2_xattr_ref slab objects; per guidance a UAF enables arbitrary kernel memory disclosure.\nI:H - The second pass double-frees attacker-populated jffs2_xattr_ref objects, enabling classic heap spraying and overlapping allocations for arbitrary write / control-flow hijack.\nA:H - The KASAN-confirmed use-after-free during mount produces a kernel oops/panic even without full exploitation, and is repeatable on every mount of the crafted image."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T08:48:47.063Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/9150cb625b46f68d524f4cfd491f1aafc23e10a9"
        },
        {
          "url": "https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5"
        },
        {
          "url": "https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101"
        },
        {
          "url": "https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422"
        },
        {
          "url": "https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13"
        },
        {
          "url": "https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1"
        },
        {
          "url": "https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44"
        },
        {
          "url": "https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed"
        },
        {
          "url": "https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c"
        }
      ],
      "title": "jffs2: fix use-after-free in jffs2_clear_xattr_subsystem",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2021-47656",
    "datePublished": "2025-02-26T01:54:20.069Z",
    "dateReserved": "2025-02-26T01:48:21.521Z",
    "dateUpdated": "2026-08-05T08:48:47.063Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

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.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.