{"id":"CVE-2026-64448","revision":null,"records":[{"revision":"5b70d23b4f074762915f642540400f8c","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-64448","aliases":[],"title":"smb: client: restrict implied bcc[0] exemption to responses without data area","description":"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 \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 \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 \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 \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---","state":0,"publishedAt":"2026-07-25T08:51:18.796+00:00","modifiedAt":"2026-10-19T20:38:30.137+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"unaffected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"fs/smb/client/smb2misc.c\"\n ],\n \"versions\": [\n {\n \"version\": \"093b2bdad3221e3fae3c26d89387e7297a157664\",\n \"lessThan\": \"8d0bbc78046d264bbf6a574ea6f9072258a43e35\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"093b2bdad3221e3fae3c26d89387e7297a157664\",\n \"lessThan\": \"b6a381c01e2ac98a48e32ac0f2a45bbadd9e26b0\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"093b2bdad3221e3fae3c26d89387e7297a157664\",\n \"lessThan\": \"31c6312608c60b72a1feb99a5afb680645a3e8a3\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"093b2bdad3221e3fae3c26d89387e7297a157664\",\n \"lessThan\": \"573e502d14714d2947e22e7eff40ec20a6a44a42\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"093b2bdad3221e3fae3c26d89387e7297a157664\",\n \"lessThan\": \"419ec1b604d7fb60c10aec2dc062371f9fcd4940\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"093b2bdad3221e3fae3c26d89387e7297a157664\",\n \"lessThan\": \"ceb875a375dedbf51c9425c1d13a2d7a8435c08c\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"093b2bdad3221e3fae3c26d89387e7297a157664\",\n \"lessThan\": \"6e9d10f62773b99bd927940fd9cbdfe7207e23ff\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"093b2bdad3221e3fae3c26d89387e7297a157664\",\n \"lessThan\": \"53b7c271f06be4dd5cfc8c6ef552a8355c891a7f\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n }\n ]\n }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"affected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"fs/smb/client/smb2misc.c\"\n ],\n \"versions\": [\n {\n \"version\": \"3.6\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"3.6\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.10.261\",\n \"lessThanOrEqual\": \"5.10.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.15.212\",\n \"lessThanOrEqual\": \"5.15.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.1.178\",\n \"lessThanOrEqual\": \"6.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.6.145\",\n \"lessThanOrEqual\": \"6.6.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.12.96\",\n \"lessThanOrEqual\": \"6.12.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.18.39\",\n \"lessThanOrEqual\": \"6.18.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.1.4\",\n \"lessThanOrEqual\": \"7.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.2\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H","score":8.2,"severity":"HIGH"}],"references":["https://git.kernel.org/stable/c/8d0bbc78046d264bbf6a574ea6f9072258a43e35","https://git.kernel.org/stable/c/b6a381c01e2ac98a48e32ac0f2a45bbadd9e26b0","https://git.kernel.org/stable/c/31c6312608c60b72a1feb99a5afb680645a3e8a3","https://git.kernel.org/stable/c/573e502d14714d2947e22e7eff40ec20a6a44a42","https://git.kernel.org/stable/c/419ec1b604d7fb60c10aec2dc062371f9fcd4940","https://git.kernel.org/stable/c/ceb875a375dedbf51c9425c1d13a2d7a8435c08c","https://git.kernel.org/stable/c/6e9d10f62773b99bd927940fd9cbdfe7207e23ff","https://git.kernel.org/stable/c/53b7c271f06be4dd5cfc8c6ef552a8355c891a7f"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-64448","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-64448","identifiers":["CVE-2026-64448"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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