CVE-2026-64448 (GCVE-0-2026-64448)
Vulnerability from cvelistv5
Published
2026-07-25 08:51
Modified
2026-08-17 04:55
Severity ?
8.2 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
Summary
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[]). 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---
References
Impacted products
Vendor Product Version
Linux Linux Version: 093b2bdad3221e3fae3c26d89387e7297a157664
Version: 093b2bdad3221e3fae3c26d89387e7297a157664
Version: 093b2bdad3221e3fae3c26d89387e7297a157664
Version: 093b2bdad3221e3fae3c26d89387e7297a157664
Version: 093b2bdad3221e3fae3c26d89387e7297a157664
Version: 093b2bdad3221e3fae3c26d89387e7297a157664
Version: 093b2bdad3221e3fae3c26d89387e7297a157664
Version: 093b2bdad3221e3fae3c26d89387e7297a157664
 Create a notification for this product.
Show details on NVD website

To clipboard 

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/smb2misc.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "8d0bbc78046d264bbf6a574ea6f9072258a43e35",
              "status": "affected",
              "version": "093b2bdad3221e3fae3c26d89387e7297a157664",
              "versionType": "git"
            },
            {
              "lessThan": "b6a381c01e2ac98a48e32ac0f2a45bbadd9e26b0",
              "status": "affected",
              "version": "093b2bdad3221e3fae3c26d89387e7297a157664",
              "versionType": "git"
            },
            {
              "lessThan": "31c6312608c60b72a1feb99a5afb680645a3e8a3",
              "status": "affected",
              "version": "093b2bdad3221e3fae3c26d89387e7297a157664",
              "versionType": "git"
            },
            {
              "lessThan": "573e502d14714d2947e22e7eff40ec20a6a44a42",
              "status": "affected",
              "version": "093b2bdad3221e3fae3c26d89387e7297a157664",
              "versionType": "git"
            },
            {
              "lessThan": "419ec1b604d7fb60c10aec2dc062371f9fcd4940",
              "status": "affected",
              "version": "093b2bdad3221e3fae3c26d89387e7297a157664",
              "versionType": "git"
            },
            {
              "lessThan": "ceb875a375dedbf51c9425c1d13a2d7a8435c08c",
              "status": "affected",
              "version": "093b2bdad3221e3fae3c26d89387e7297a157664",
              "versionType": "git"
            },
            {
              "lessThan": "6e9d10f62773b99bd927940fd9cbdfe7207e23ff",
              "status": "affected",
              "version": "093b2bdad3221e3fae3c26d89387e7297a157664",
              "versionType": "git"
            },
            {
              "lessThan": "53b7c271f06be4dd5cfc8c6ef552a8355c891a7f",
              "status": "affected",
              "version": "093b2bdad3221e3fae3c26d89387e7297a157664",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/smb2misc.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "3.6"
            },
            {
              "lessThan": "3.6",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.261",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.212",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.178",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.145",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.96",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.39",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.261",
                  "versionStartIncluding": "3.6",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.212",
                  "versionStartIncluding": "3.6",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.178",
                  "versionStartIncluding": "3.6",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.145",
                  "versionStartIncluding": "3.6",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.96",
                  "versionStartIncluding": "3.6",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.39",
                  "versionStartIncluding": "3.6",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1.4",
                  "versionStartIncluding": "3.6",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2",
                  "versionStartIncluding": "3.6",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "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   \u003cTASK\u003e\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   \u003c/TASK\u003e\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   \u003cTASK\u003e\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   \u003c/TASK\u003e\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---"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.2,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - A malicious or compromised SMB server can trigger the flaw through crafted TCP responses, typically over port 445.\nAC:L - The server directly controls the frame length, data offset, and declared data length, so no race or condition outside the attacker\u0027s control is required.\nPR:N - NEGOTIATE and SESSION_SETUP responses are processed before authentication and signature verification, requiring no attacker credentials or local capabilities.\nUI:N - An existing persistent SMB mount automatically renegotiates after a server-induced reconnect, allowing exploitation without contemporaneous user action.\nS:U - The vulnerable SMB decoder and resulting kernel impact remain within the host kernel\u0027s security authority.\nC:L - The discrepancy permits exactly one byte beyond the received data to be read; the NTLM path can preserve and reflect that byte in subsequent authentication data, but the disclosure is strictly bounded.\nI:N - The flaw performs an out-of-bounds read and copies data into valid allocations; it provides no out-of-bounds write or other demonstrated memory-modification primitive.\nA:H - The demonstrated slab out-of-bounds access raises a KASAN BUG and can panic hardened kernels, and a malicious peer can retrigger it during negotiation or reconnection."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:55:51.813Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "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"
        }
      ],
      "title": "smb: client: restrict implied bcc[0] exemption to responses without data area",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64448",
    "datePublished": "2026-07-25T08:51:18.796Z",
    "dateReserved": "2026-07-19T15:36:31.788Z",
    "dateUpdated": "2026-08-17T04:55:51.813Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
  • Confirmed: The vulnerability is confirmed from an analyst perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
  • Patched: This vulnerability was successfully patched by the user reporting the sighting.
  • Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
  • Not confirmed: The user expresses doubt about the veracity of the vulnerability.
  • Not patched: This vulnerability was not successfully patched by the user reporting the sighting.