smb: client: restrict implied bcc[0] exemption to responses without data area

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-64448
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-25 10:17:29 UTC
Updated2026-09-03 15:34:28 UTC
DescriptionIn 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[]). 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: 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 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---

Risk And Classification

Primary CVSS: v3.1 8.2 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

EPSS: 0.004630000 probability, percentile 0.382060000 (date 2026-08-17)

Problem Types: CWE-125

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary8.2HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
3.1CNADECLARED8.2HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 093b2bdad3221e3fae3c26d89387e7297a157664 8d0bbc78046d264bbf6a574ea6f9072258a43e35 git Not specified
CNA Linux Linux affected 093b2bdad3221e3fae3c26d89387e7297a157664 b6a381c01e2ac98a48e32ac0f2a45bbadd9e26b0 git Not specified
CNA Linux Linux affected 093b2bdad3221e3fae3c26d89387e7297a157664 31c6312608c60b72a1feb99a5afb680645a3e8a3 git Not specified
CNA Linux Linux affected 093b2bdad3221e3fae3c26d89387e7297a157664 573e502d14714d2947e22e7eff40ec20a6a44a42 git Not specified
CNA Linux Linux affected 093b2bdad3221e3fae3c26d89387e7297a157664 419ec1b604d7fb60c10aec2dc062371f9fcd4940 git Not specified
CNA Linux Linux affected 093b2bdad3221e3fae3c26d89387e7297a157664 ceb875a375dedbf51c9425c1d13a2d7a8435c08c git Not specified
CNA Linux Linux affected 093b2bdad3221e3fae3c26d89387e7297a157664 6e9d10f62773b99bd927940fd9cbdfe7207e23ff git Not specified
CNA Linux Linux affected 093b2bdad3221e3fae3c26d89387e7297a157664 53b7c271f06be4dd5cfc8c6ef552a8355c891a7f git Not specified
CNA Linux Linux affected 3.6 Not specified
CNA Linux Linux unaffected 3.6 semver Not specified
CNA Linux Linux unaffected 5.10.261 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.212 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.178 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.145 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.96 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.39 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.4 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/6e9d10f62773b99bd927940fd9cbdfe7207e23ff 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/8d0bbc78046d264bbf6a574ea6f9072258a43e35 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/ceb875a375dedbf51c9425c1d13a2d7a8435c08c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/53b7c271f06be4dd5cfc8c6ef552a8355c891a7f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/573e502d14714d2947e22e7eff40ec20a6a44a42 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/419ec1b604d7fb60c10aec2dc062371f9fcd4940 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/31c6312608c60b72a1feb99a5afb680645a3e8a3 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/b6a381c01e2ac98a48e32ac0f2a45bbadd9e26b0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

© CVE.report 2026

Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties, implied or otherwise, with regard to this information or its use. Any use of this information is at the user's risk. It is the responsibility of user to evaluate the accuracy, completeness or usefulness of any information, opinion, advice or other content. EACH USER WILL BE SOLELY RESPONSIBLE FOR ANY consequences of his or her direct or indirect use of this web site. ALL WARRANTIES OF ANY KIND ARE EXPRESSLY DISCLAIMED. This site will NOT BE LIABLE FOR ANY DIRECT, INDIRECT or any other kind of loss.

CVE, CWE, and OVAL are registred trademarks of The MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. This site includes MITRE data granted under the following license.

Free CVE JSON API cve.report/api

CVE.report and Source URL Uptime Status status.cve.report