{"id":"CVE-2026-64448","title":"smb: client: restrict implied bcc[0] exemption to responses without data area","summary":"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 l…","severity":"high","cvss":8.2,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 8d0bbc78046d264bbf6a574ea6f9072258a43e35","Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < b6a381c01e2ac98a48e32ac0f2a45bbadd9e26b0","Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 31c6312608c60b72a1feb99a5afb680645a3e8a3","Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 573e502d14714d2947e22e7eff40ec20a6a44a42","Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 419ec1b604d7fb60c10aec2dc062371f9fcd4940","Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < ceb875a375dedbf51c9425c1d13a2d7a8435c08c","Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 6e9d10f62773b99bd927940fd9cbdfe7207e23ff","Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 53b7c271f06be4dd5cfc8c6ef552a8355c891a7f","Linux 3.6"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-10-16T15:41:01.162608Z"},"published":"2026-07-25","updated":"2026-10-16","sourceUpdated":"2026-10-16T15:42:37.026Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-64448","references":[{"url":"https://git.kernel.org/stable/c/8d0bbc78046d264bbf6a574ea6f9072258a43e35"},{"url":"https://git.kernel.org/stable/c/b6a381c01e2ac98a48e32ac0f2a45bbadd9e26b0"},{"url":"https://git.kernel.org/stable/c/31c6312608c60b72a1feb99a5afb680645a3e8a3"},{"url":"https://git.kernel.org/stable/c/573e502d14714d2947e22e7eff40ec20a6a44a42"},{"url":"https://git.kernel.org/stable/c/419ec1b604d7fb60c10aec2dc062371f9fcd4940"},{"url":"https://git.kernel.org/stable/c/ceb875a375dedbf51c9425c1d13a2d7a8435c08c"},{"url":"https://git.kernel.org/stable/c/6e9d10f62773b99bd927940fd9cbdfe7207e23ff"},{"url":"https://git.kernel.org/stable/c/53b7c271f06be4dd5cfc8c6ef552a8355c891a7f"}],"tags":["cve.org"],"epss":0.00463,"epssPercentile":0.38687,"ingestedAt":"2026-10-16T17:24:46.821Z","slug":"CVE-2026-64448","body":"## Overview\n\nIn 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---\n\n## Affected\n\n- `Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 8d0bbc78046d264bbf6a574ea6f9072258a43e35`\n- `Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < b6a381c01e2ac98a48e32ac0f2a45bbadd9e26b0`\n- `Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 31c6312608c60b72a1feb99a5afb680645a3e8a3`\n- `Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 573e502d14714d2947e22e7eff40ec20a6a44a42`\n- `Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 419ec1b604d7fb60c10aec2dc062371f9fcd4940`\n- `Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < ceb875a375dedbf51c9425c1d13a2d7a8435c08c`\n- `Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 6e9d10f62773b99bd927940fd9cbdfe7207e23ff`\n- `Linux >= 093b2bdad3221e3fae3c26d89387e7297a157664 < 53b7c271f06be4dd5cfc8c6ef552a8355c891a7f`\n- `Linux 3.6`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":45,"depthScoreParts":{"impact":45.1,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}