CVE-2026-64448
Estado: AnalizadaAlta (8.2)—
In the Linux kernel, the following vulnerability has been resolved:
smb: client: restrict implied bcc[0] exemption to responses without data area
smb2_check_message() has a long-standing quirk that accepts a response whose calculated length is one byte larger than the bytes actually received ("server can return one byte more due to implied bcc[0]"). This was introduced to accommodate servers that omit the trailing bcc[0] overlap byte when no data area is present.
However, the exemption is applied unconditionally, regardless of whether the command actually carries a data area (has_smb2_data_area[]).
Leer descripción completaMostrar menos
When a response with a data area is subject to the +1 exemption, the reported data can extend one byte beyond the bytes actually received, yet smb2_check_message() still accepts it. The subsequent decoder then reads past the end of the receive buffer. This is reachable during NEGOTIATE and SESSION_SETUP, before the session is established.
The resulting out-of-bounds reads are visible under KASAN when mounting against a non-conforming server; both the SPNEGO/negTokenInit and the NTLMSSP challenge decoders are affected:
Restrict the +1 exemption to responses that have no data area, so that it still covers the bcc[0] omission it was meant for. When a data area is present, the +1 discrepancy instead means the reported data length overruns the ---truncated---
Detalles técnicos trazas, registros y código del informe original
BUG: KASAN: slab-out-of-bounds in asn1_ber_decoder+0x16a7/0x1b00 Read of size 1 at addr ffff8880084d67c0 by task mount.cifs/81 CPU: 1 UID: 0 PID: 81 Comm: mount.cifs Not tainted 7.1.0-rc6 #1 Call Trace: <TASK> dump_stack_lvl+0x4e/0x70 print_report+0x157/0x4c9 kasan_report+0xce/0x100 asn1_ber_decoder+0x16a7/0x1b00 decode_negTokenInit+0x19/0x30 SMB2_negotiate+0x31d9/0x4c90 cifs_negotiate_protocol+0x1f2/0x3f0 cifs_get_smb_ses+0x93f/0x17e0 cifs_mount_get_session+0x7f/0x3a0 cifs_mount+0xb4/0xcf0 cifs_smb3_do_mount+0x23a/0x1500 smb3_get_tree+0x3b0/0x630 vfs_get_tree+0x82/0x2d0 fc_mount+0x10/0x1b0 path_mount+0x50d/0x1de0 __x64_sys_mount+0x20b/0x270 do_syscall_64+0xee/0x590 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> Allocated by task 85: kmem_cache_alloc_noprof+0x106/0x380 mempool_alloc_noprof+0x116/0x1e0 cifs_small_buf_get+0x31/0x80 allocate_buffers+0x10d/0x2b0 cifs_demultiplex_thread+0x1d5/0x1d50 kthread+0x2c6/0x390 ret_from_fork+0x36e/0x5a0 ret_from_fork_asm+0x1a/0x30 The buggy address is located 0 bytes to the right of allocated 448-byte region [ffff8880084d6600, ffff8880084d67c0) which belongs to the cache cifs_small_rq of size 448 BUG: KASAN: slab-out-of-bounds in kmemdup_noprof+0x36/0x50 Read of size 329 at addr ffff88800726c678 by task mount.cifs/89 CPU: 0 UID: 0 PID: 89 Comm: mount.cifs Tainted: G B 7.1.0-rc6 #1 Call Trace: <TASK> dump_stack_lvl+0x4e/0x70 print_report+0x157/0x4c9 kasan_report+0xce/0x100 kasan_check_range+0x10f/0x1e0 __asan_memcpy+0x23/0x60 kmemdup_noprof+0x36/0x50 decode_ntlmssp_challenge+0x457/0x680 SMB2_sess_auth_rawntlmssp_negotiate+0x6f0/0xcb0 SMB2_sess_setup+0x219/0x4f0 cifs_setup_session+0x248/0xaf0 cifs_get_smb_ses+0xf79/0x17e0 cifs_mount_get_session+0x7f/0x3a0 cifs_mount+0xb4/0xcf0 cifs_smb3_do_mount+0x23a/0x1500 smb3_get_tree+0x3b0/0x630 vfs_get_tree+0x82/0x2d0 fc_mount+0x10/0x1b0 path_mount+0x50d/0x1de0 __x64_sys_mount+0x20b/0x270 do_syscall_64+0xee/0x590 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> Allocated by task 93: kmem_cache_alloc_noprof+0x106/0x380 mempool_alloc_noprof+0x116/0x1e0 cifs_small_buf_get+0x31/0x80 allocate_buffers+0x10d/0x2b0 cifs_demultiplex_thread+0x1d5/0x1d50 kthread+0x2c6/0x390 ret_from_fork+0x36e/0x5a0 ret_from_fork_asm+0x1a/0x30 The buggy address is located 120 bytes inside of allocated 448-byte region [ffff88800726c600, ffff88800726c7c0) which belongs to the cache cifs_small_rq of size 448
CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
- Puntuación base: 8.2
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.63%
- Percentil entre todas las CVEs puntuadas: 49
- 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
T1190Exploit Public-Facing Applicationinitial access75 % - Impacto principal
T1005Data from Local Systemcollection85 % - Impacto secundario
T1499.004Application or System Exploitationimpact65 %
Vulnerabilidad de lectura fuera de límites (CWE-125) en cliente SMB2 del kernel Linux accesible remotamente sin autenticación (AV:N/PR:N/UI:N). Permite leer datos de buffer del kernel durante NEGOTIATE/SESSION_SETUP, causando denegación de servicio (HIGH impact en A) y potencial exfiltración de dato
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-125
Referencias
- https://git.kernel.org/stable/c/31c6312608c60b72a1feb99a5afb680645a3e8a3
- https://git.kernel.org/stable/c/419ec1b604d7fb60c10aec2dc062371f9fcd4940
- https://git.kernel.org/stable/c/53b7c271f06be4dd5cfc8c6ef552a8355c891a7f
- https://git.kernel.org/stable/c/573e502d14714d2947e22e7eff40ec20a6a44a42
- https://git.kernel.org/stable/c/6e9d10f62773b99bd927940fd9cbdfe7207e23ff
- https://git.kernel.org/stable/c/8d0bbc78046d264bbf6a574ea6f9072258a43e35
- https://git.kernel.org/stable/c/b6a381c01e2ac98a48e32ac0f2a45bbadd9e26b0
- https://git.kernel.org/stable/c/ceb875a375dedbf51c9425c1d13a2d7a8435c08c
JSON original (NVD)
Mostrar
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"published": "2026-07-25T10:17:29.557",
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"source": "nvd@nist.gov",
"description": [
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"value": "CWE-125"
}
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}
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: restrict implied bcc[0] exemption to responses without data area\n\nsmb2_check_message() has a long-standing quirk that accepts a response\nwhose calculated length is one byte larger than the bytes actually\nreceived (\"server can return one byte more due to implied bcc[0]\").\nThis was introduced to accommodate servers that omit the trailing bcc[0]\noverlap byte when no data area is present.\n\nHowever, the exemption is applied unconditionally, regardless of whether\nthe command actually carries a data area (has_smb2_data_area[]). When a\nresponse with a data area is subject to the +1 exemption, the reported\ndata can extend one byte beyond the bytes actually received, yet\nsmb2_check_message() still accepts it. The subsequent decoder then reads\npast the end of the receive buffer. This is reachable during NEGOTIATE\nand SESSION_SETUP, before the session is established.\n\nThe resulting out-of-bounds reads are visible under KASAN when mounting\nagainst a non-conforming server; both the SPNEGO/negTokenInit and the\nNTLMSSP challenge decoders are affected:\n\n BUG: KASAN: slab-out-of-bounds in asn1_ber_decoder+0x16a7/0x1b00\n Read of size 1 at addr ffff8880084d67c0 by task mount.cifs/81\n CPU: 1 UID: 0 PID: 81 Comm: mount.cifs Not tainted 7.1.0-rc6 #1\n Call Trace:\n <TASK>\n dump_stack_lvl+0x4e/0x70\n print_report+0x157/0x4c9\n kasan_report+0xce/0x100\n asn1_ber_decoder+0x16a7/0x1b00\n decode_negTokenInit+0x19/0x30\n SMB2_negotiate+0x31d9/0x4c90\n cifs_negotiate_protocol+0x1f2/0x3f0\n cifs_get_smb_ses+0x93f/0x17e0\n cifs_mount_get_session+0x7f/0x3a0\n cifs_mount+0xb4/0xcf0\n cifs_smb3_do_mount+0x23a/0x1500\n smb3_get_tree+0x3b0/0x630\n vfs_get_tree+0x82/0x2d0\n fc_mount+0x10/0x1b0\n path_mount+0x50d/0x1de0\n __x64_sys_mount+0x20b/0x270\n do_syscall_64+0xee/0x590\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\n </TASK>\n Allocated by task 85:\n kmem_cache_alloc_noprof+0x106/0x380\n mempool_alloc_noprof+0x116/0x1e0\n cifs_small_buf_get+0x31/0x80\n allocate_buffers+0x10d/0x2b0\n cifs_demultiplex_thread+0x1d5/0x1d50\n kthread+0x2c6/0x390\n ret_from_fork+0x36e/0x5a0\n ret_from_fork_asm+0x1a/0x30\n The buggy address is located 0 bytes to the right of\n allocated 448-byte region [ffff8880084d6600, ffff8880084d67c0)\n which belongs to the cache cifs_small_rq of size 448\n\n BUG: KASAN: slab-out-of-bounds in kmemdup_noprof+0x36/0x50\n Read of size 329 at addr ffff88800726c678 by task mount.cifs/89\n CPU: 0 UID: 0 PID: 89 Comm: mount.cifs Tainted: G B 7.1.0-rc6 #1\n Call Trace:\n <TASK>\n dump_stack_lvl+0x4e/0x70\n print_report+0x157/0x4c9\n kasan_report+0xce/0x100\n kasan_check_range+0x10f/0x1e0\n __asan_memcpy+0x23/0x60\n kmemdup_noprof+0x36/0x50\n decode_ntlmssp_challenge+0x457/0x680\n SMB2_sess_auth_rawntlmssp_negotiate+0x6f0/0xcb0\n SMB2_sess_setup+0x219/0x4f0\n cifs_setup_session+0x248/0xaf0\n cifs_get_smb_ses+0xf79/0x17e0\n cifs_mount_get_session+0x7f/0x3a0\n cifs_mount+0xb4/0xcf0\n cifs_smb3_do_mount+0x23a/0x1500\n smb3_get_tree+0x3b0/0x630\n vfs_get_tree+0x82/0x2d0\n fc_mount+0x10/0x1b0\n path_mount+0x50d/0x1de0\n __x64_sys_mount+0x20b/0x270\n do_syscall_64+0xee/0x590\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\n </TASK>\n Allocated by task 93:\n kmem_cache_alloc_noprof+0x106/0x380\n mempool_alloc_noprof+0x116/0x1e0\n cifs_small_buf_get+0x31/0x80\n allocate_buffers+0x10d/0x2b0\n cifs_demultiplex_thread+0x1d5/0x1d50\n kthread+0x2c6/0x390\n ret_from_fork+0x36e/0x5a0\n ret_from_fork_asm+0x1a/0x30\n The buggy address is located 120 bytes inside of\n allocated 448-byte region [ffff88800726c600, ffff88800726c7c0)\n which belongs to the cache cifs_small_rq of size 448\n\nRestrict the +1 exemption to responses that have no data area, so that\nit still covers the bcc[0] omission it was meant for. When a data area\nis present, the +1 discrepancy instead means the reported data length\noverruns the\n---truncated---"
}
],
"lastModified": "2026-09-03T15:34:28.527",
"configurations": [
{
"nodes": [
{
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