CVE-2026-63794
Estado: AnalizadaAlta (7.8)—
In the Linux kernel, the following vulnerability has been resolved:
KVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path
In sev_dbg_crypt(), the per-iteration transfer length is bounded by the source page offset (PAGE_SIZE - s_off) but not by the destination page offset (PAGE_SIZE - d_off). When d_off > s_off, the encrypt path (__sev_dbg_encrypt_user) performs a read-modify-write using a single-page intermediate buffer (dst_tpage):
Trigger example: s_off = 0, d_off = 1, debug.len = PAGE_SIZE - the PSP is instructed to write round_up(4097, 16) = 4112 bytes to a 4096-byte buffer.
Fix by also bounding len by (PAGE_SIZE - d_off), the same check that sev_send_update_data() already performs for its single-page guest region.
Leer descripción completaMostrar menos
The buggy address belongs to the physical page: page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x7fe72b6a0 pfn:0x62293bb memcg:ff11000112827d82 flags: 0x1400000000000000(node=1|zone=1) raw: 1400000000000000 0000000000000000 dead000000000122 0000000000000000 raw: 00000007fe72b6a0 0000000000000000 00000001ffffffff ff11000112827d82 page dumped because: kasan: bad access detected
[sean: add sample KASAN splat, Fixes, and stable@]
Detalles técnicos trazas, registros y código del informe original
1. __sev_dbg_decrypt() expands the size to round_up(len + (d_off & 15), 16)
before issuing the PSP command. If len + (d_off & 15) > PAGE_SIZE,
the PSP writes beyond the end of the 4096-byte dst_tpage allocation.
2. The subsequent memcpy()/copy_from_user() into
page_address(dst_tpage) + (d_off & 15) of 'len' bytes overflows
by up to 15 bytes under the same condition.
==================================================================
BUG: KASAN: slab-use-after-free in sev_dbg_crypt+0x993/0xd10 [kvm_amd]
Write of size 4095 at addr ff110062293bb009 by task sev_dbg_test/228214
CPU: 96 UID: 0 PID: 228214 Comm: sev_dbg_test Tainted: G U W 7.0.0-smp--5ce9b0c48211-dbg #156 PREEMPTLAZY
Tainted: [U]=USER, [W]=WARN
Hardware name: Google Astoria/astoria, BIOS 0.20250817.1-0 08/25/2025
Call Trace:
<TASK>
dump_stack_lvl+0x54/0x70
print_report+0xbc/0x260
kasan_report+0xa2/0xd0
kasan_check_range+0x25f/0x2c0
__asan_memcpy+0x40/0x70
sev_dbg_crypt+0x993/0xd10 [kvm_amd]
sev_mem_enc_ioctl+0x33c/0x450 [kvm_amd]
kvm_vm_ioctl+0x65d/0x6d0 [kvm]
__se_sys_ioctl+0xb2/0x100
do_syscall_64+0xe8/0x870
entry_SYSCALL_64_after_hwframe+0x4b/0x53
</TASK>
Memory state around the buggy address:
ff110062293bbf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ff110062293bbf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ff110062293bc000: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
^
ff110062293bc080: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ff110062293bc100: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================
Disabling lock debugging due to kernel taintCVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Puntuación base: 7.8
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.14%
- Percentil entre todas las CVEs puntuadas: 3
- Fecha de la puntuación: 6/10/2026
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
T1068Exploitation for Privilege Escalationprivilege escalation85 % - Impacto principal
T1059Command and Scripting Interpreterexecution75 %
Buffer overflow en código de kernel (CWE-787) accesible por usuario local sin interacción (AV:L, PR:L, UI:N). Permite ejecución de código arbitrario con privilegios del 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-787
Referencias
- https://git.kernel.org/stable/c/2753a097d1fe24c4351c608048612c74108aa89f
- https://git.kernel.org/stable/c/64f2449841ffc7d203183aa4c748c9c77951ecc5
- https://git.kernel.org/stable/c/720949ed666f34ff28ffdfe1471a5861d1e41fdf
- https://git.kernel.org/stable/c/78ee2d50185a037b3d2452a97f3dad69c3f7f389
- https://git.kernel.org/stable/c/889c2a9c59897ca912bf39df5bb92555a0a13df4
- https://git.kernel.org/stable/c/9349b50f4b11f135fe73b56cb2c2c872d8bc71d7
- https://git.kernel.org/stable/c/e1a0fe288dee07b7da25a71e007c1ecd1080315b
- https://git.kernel.org/stable/c/f701ae476cb92a3a3d8844bb39bb63b4512684c8
JSON original (NVD)
Mostrar
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path\n\nIn sev_dbg_crypt(), the per-iteration transfer length is bounded by\nthe source page offset (PAGE_SIZE - s_off) but not by the destination\npage offset (PAGE_SIZE - d_off). When d_off > s_off, the encrypt\npath (__sev_dbg_encrypt_user) performs a read-modify-write using a\nsingle-page intermediate buffer (dst_tpage):\n\n 1. __sev_dbg_decrypt() expands the size to round_up(len + (d_off & 15), 16)\n before issuing the PSP command. If len + (d_off & 15) > PAGE_SIZE,\n the PSP writes beyond the end of the 4096-byte dst_tpage allocation.\n\n 2. The subsequent memcpy()/copy_from_user() into\n page_address(dst_tpage) + (d_off & 15) of 'len' bytes overflows\n by up to 15 bytes under the same condition.\n\nTrigger example: s_off = 0, d_off = 1, debug.len = PAGE_SIZE -\nthe PSP is instructed to write round_up(4097, 16) = 4112 bytes to\na 4096-byte buffer.\n\nFix by also bounding len by (PAGE_SIZE - d_off), the same check that\nsev_send_update_data() already performs for its single-page guest\nregion.\n\n ==================================================================\n BUG: KASAN: slab-use-after-free in sev_dbg_crypt+0x993/0xd10 [kvm_amd]\n Write of size 4095 at addr ff110062293bb009 by task sev_dbg_test/228214\n\n CPU: 96 UID: 0 PID: 228214 Comm: sev_dbg_test Tainted: G U W 7.0.0-smp--5ce9b0c48211-dbg #156 PREEMPTLAZY\n Tainted: [U]=USER, [W]=WARN\n Hardware name: Google Astoria/astoria, BIOS 0.20250817.1-0 08/25/2025\n Call Trace:\n <TASK>\n dump_stack_lvl+0x54/0x70\n print_report+0xbc/0x260\n kasan_report+0xa2/0xd0\n kasan_check_range+0x25f/0x2c0\n __asan_memcpy+0x40/0x70\n sev_dbg_crypt+0x993/0xd10 [kvm_amd]\n sev_mem_enc_ioctl+0x33c/0x450 [kvm_amd]\n kvm_vm_ioctl+0x65d/0x6d0 [kvm]\n __se_sys_ioctl+0xb2/0x100\n do_syscall_64+0xe8/0x870\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n </TASK>\n\n The buggy address belongs to the physical page:\n page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x7fe72b6a0 pfn:0x62293bb\n memcg:ff11000112827d82\n flags: 0x1400000000000000(node=1|zone=1)\n raw: 1400000000000000 0000000000000000 dead000000000122 0000000000000000\n raw: 00000007fe72b6a0 0000000000000000 00000001ffffffff ff11000112827d82\n page dumped because: kasan: bad access detected\n\n Memory state around the buggy address:\n ff110062293bbf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00\n ff110062293bbf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00\n >ff110062293bc000: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc\n ^\n ff110062293bc080: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc\n ff110062293bc100: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc\n ==================================================================\n Disabling lock debugging due to kernel taint\n\n[sean: add sample KASAN splat, Fixes, and stable@]"
}
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"lastModified": "2026-08-17T05:17:15.500",
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