CVE-2021-47656
Estado: ModificadaAlta (7.8)—
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().
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.
Leer descripción completaMostrar menos
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.
Detalles técnicos trazas, registros y código del informe original
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
-----------------------------------------------------------CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- Puntuación base: 7.8
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.26%
- Percentil entre todas las CVEs puntuadas: 16
- Fecha de la puntuación: 5/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
🎯 Técnicas ATT&CK
Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.
- Explotación
T1203Exploitation for Client Executionexecution75 % - Impacto principal
T1068Exploitation for Privilege Escalationprivilege escalation80 %
Use-after-free en kernel de Linux (CWE-416) que requiere montaje de imagen malformada; acceso local con interacción del usuario (UI:R). El impacto es escalada de privilegios via corrupción de memoria en el kernel.
Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.
🛡️ Mitigaciones ATT&CK que cubren estas técnicas
Tecnologías afectadas (1)
CWE
- CWE-416
Referencias
- https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44
- https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422
- https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5
- https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c
- https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1
- https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13
- https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed
- https://git.kernel.org/stable/c/9150cb625b46f68d524f4cfd491f1aafc23e10a9
- https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101
JSON original (NVD)
Mostrar
{
"id": "CVE-2021-47656",
"cveTags": [],
"metrics": {
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2021-47656",
"role": "CISA Coordinator",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "total"
}
],
"version": "2.0.3",
"timestamp": "2025-02-27T17:59:35.381270Z"
}
}
],
"cvssMetricV31": [
{
"type": "Secondary",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"cvssData": {
"scope": "UNCHANGED",
"version": "3.1",
"baseScore": 7.8,
"attackVector": "LOCAL",
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
"integrityImpact": "HIGH",
"userInteraction": "REQUIRED",
"attackComplexity": "LOW",
"availabilityImpact": "HIGH",
"privilegesRequired": "NONE",
"confidentialityImpact": "HIGH"
},
"impactScore": 5.9,
"exploitabilityScore": 1.8
},
{
"type": "Secondary",
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"cvssData": {
"scope": "UNCHANGED",
"version": "3.1",
"baseScore": 7.8,
"attackVector": "LOCAL",
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"integrityImpact": "HIGH",
"userInteraction": "NONE",
"attackComplexity": "LOW",
"availabilityImpact": "HIGH",
"privilegesRequired": "LOW",
"confidentialityImpact": "HIGH"
},
"impactScore": 5.9,
"exploitabilityScore": 1.8
}
]
},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
"lessThan": "9150cb625b46f68d524f4cfd491f1aafc23e10a9",
"versionType": "git"
},
{
"status": "affected",
"version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
"lessThan": "3bd2454162ec6bbb5503233c804fce6e4b6dcec5",
"versionType": "git"
},
{
"status": "affected",
"version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
"lessThan": "c3b07c875fa8f906f932976460fd14798596f101",
"versionType": "git"
},
{
"status": "affected",
"version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
"lessThan": "30bf7244acf32f19cb722c39f7bc1c2a9f300422",
"versionType": "git"
},
{
"status": "affected",
"version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
"lessThan": "7bb7428dd73991bf4b3a7a61b493ca50046c2b13",
"versionType": "git"
},
{
"status": "affected",
"version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
"lessThan": "7a75740206af5f17e9f3efa384211cba70213da1",
"versionType": "git"
},
{
"status": "affected",
"version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
"lessThan": "22327bd7988f21de3a53c1373f3b81542bfe1f44",
"versionType": "git"
},
{
"status": "affected",
"version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
"lessThan": "8c0f024f29e055840a5a89fe23b96ae3f921afed",
"versionType": "git"
},
{
"status": "affected",
"version": "aa98d7cf59b5b0764d3502662053489585faf2fe",
"lessThan": "4c7c44ee1650677fbe89d86edbad9497b7679b5c",
"versionType": "git"
}
],
"programFiles": [
"fs/jffs2/fs.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "2.6.18"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "2.6.18",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "4.9.311",
"versionType": "semver",
"lessThanOrEqual": "4.9.*"
},
{
"status": "unaffected",
"version": "4.14.276",
"versionType": "semver",
"lessThanOrEqual": "4.14.*"
},
{
"status": "unaffected",
"version": "4.19.238",
"versionType": "semver",
"lessThanOrEqual": "4.19.*"
},
{
"status": "unaffected",
"version": "5.4.189",
"versionType": "semver",
"lessThanOrEqual": "5.4.*"
},
{
"status": "unaffected",
"version": "5.10.110",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.33",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "5.16.19",
"versionType": "semver",
"lessThanOrEqual": "5.16.*"
},
{
"status": "unaffected",
"version": "5.17.2",
"versionType": "semver",
"lessThanOrEqual": "5.17.*"
},
{
"status": "unaffected",
"version": "5.18",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"fs/jffs2/fs.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2025-02-26T06:37:07.360",
"references": [
{
"url": "https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/9150cb625b46f68d524f4cfd491f1aafc23e10a9",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Modified",
"weaknesses": [
{
"type": "Secondary",
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"description": [
{
"lang": "en",
"value": "CWE-416"
}
]
}
],
"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 <--- ERROR\n jffs2_clear_xattr_subsystem <--- free\n jffs2_clear_xattr_subsystem <--- 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 'out_inohash' to 'out_root'\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 tamaño 8 en la dirección 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 dirección con errores pertenece al objeto en ffff8881243384b8 que pertenece al caché jffs2_xattr_ref de tamaño 48 La dirección con errores se encuentra 40 bytes dentro de la región de 48 bytes [ffff8881243384b8, ffff8881243384e8) [...] ========================================================================== La activación 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 <--- ERROR jffs2_clear_xattr_subsystem <--- free jffs2_clear_xattr_subsystem <--- 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 'out_inohash' a 'out_root' para solucionar este problema de UAF."
}
],
"lastModified": "2026-08-04T10:17:12.300",
"configurations": [
{
"nodes": [
{
"negate": false,
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "EB5E8137-261D-4D1B-A71B-A70EE8FD2C08",
"versionEndExcluding": "4.9.311",
"versionStartIncluding": "2.6.18"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "6D9B028C-6313-47F9-94B7-5F8122345E49",
"versionEndExcluding": "4.14.276",
"versionStartIncluding": "4.10"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "FA28527A-11D3-41D2-9C4C-ECAC0D6A4A2D",
"versionEndExcluding": "4.19.238",
"versionStartIncluding": "4.15"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "8CB6E8F5-C2B1-46F3-A807-0F6104AC340F",
"versionEndExcluding": "5.4.189",
"versionStartIncluding": "4.20"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "91D3BFD0-D3F3-4018-957C-96CCBF357D79",
"versionEndExcluding": "5.10.110",
"versionStartIncluding": "5.5"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "27C42AE8-B387-43E2-938A-E1C8B40BE6D5",
"versionEndExcluding": "5.15.33",
"versionStartIncluding": "5.11"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "20C43679-0439-405A-B97F-685BEE50613B",
"versionEndExcluding": "5.16.19",
"versionStartIncluding": "5.16"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "210C679C-CF84-44A3-8939-E629C87E54BF",
"versionEndExcluding": "5.17.2",
"versionStartIncluding": "5.17"
}
],
"operator": "OR"
}
]
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}