{"id":"CVE-2026-64136","state":"PUBLISHED","title":"smb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked()\n\nCommit 96c4af418586 (\"cifs: Fix locking usage for tcon fields\")\nrefactored cifs code to change cifs_tcp_ses_lock for tc_lock around\ntc_count changes.\n\nThere was missing lock around tc_count increment inside\nsmb2_find_smb_sess_tcon_unlocked().","publishedAt":"2026-07-19T15:40:30.351Z","updatedAt":"2026-10-30T12:27:35.201Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"92d197ef7e9bb4994dae2bb17c2f19fa09d219a2","status":"affected","lessThan":"7585d4242f59185b084957fa077396e53dbf7c24","versionType":"git"},{"version":"953953abb66e52c224057ab91e404284fefeab62","status":"affected","lessThan":"7df1df6f40c0720d30206aa35c0343b962350e0d","versionType":"git"},{"version":"601dd3b79769b38d30b693c40afdb2a4b7edf9d0","status":"affected","lessThan":"13fb413ae22a37c69341918a6d651d19a9b0b9b7","versionType":"git"},{"version":"3969db6b22e3d90d8c5f22ac1a7fe0350a94c136","status":"affected","lessThan":"bf4ebdb19ff9b3cdf992b50715fe61633327416a","versionType":"git"},{"version":"96c4af418586ee9a6aab61738644366426e05316","status":"affected","lessThan":"e374f4e496fef8168784f93a4477d67be34485fd","versionType":"git"},{"version":"96c4af418586ee9a6aab61738644366426e05316","status":"affected","lessThan":"4d8690dace005a38e6dbde9ecce2da3ad85c7c41","versionType":"git"},{"version":"8c59eeeeffa1524ef57e173a89a1a3ff539888d5","status":"affected","versionType":"git"},{"version":"6.6.128","status":"affected","lessThan":"6.6.142","versionType":"semver"},{"version":"6.12.75","status":"affected","lessThan":"6.12.92","versionType":"semver"},{"version":"6.18.16","status":"affected","lessThan":"6.18.34","versionType":"semver"},{"version":"6.19.6","status":"affected","lessThan":"6.20","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/client/smb2transport.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.0","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.0","versionType":"semver"},{"version":"6.6.142","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.92","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.34","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.11","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/client/smb2transport.c"]}],"references":["https://git.kernel.org/stable/c/7585d4242f59185b084957fa077396e53dbf7c24","https://git.kernel.org/stable/c/7df1df6f40c0720d30206aa35c0343b962350e0d","https://git.kernel.org/stable/c/13fb413ae22a37c69341918a6d651d19a9b0b9b7","https://git.kernel.org/stable/c/bf4ebdb19ff9b3cdf992b50715fe61633327416a","https://git.kernel.org/stable/c/e374f4e496fef8168784f93a4477d67be34485fd","https://git.kernel.org/stable/c/4d8690dace005a38e6dbde9ecce2da3ad85c7c41"],"weaknesses":["CWE-362"],"ingestedAt":"2026-10-30T12:46:06.359Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/64xxx/CVE-2026-64136.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-64136","state":"PUBLISHED","datePublished":"2026-07-19T15:40:30.351Z","dateUpdated":"2026-10-30T12:27:35.201Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-19T07:54:57.036Z"},"containers":{"cna":{"title":"smb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked()\n\nCommit 96c4af418586 (\"cifs: Fix locking usage for tcon fields\")\nrefactored cifs code to change cifs_tcp_ses_lock for tc_lock around\ntc_count changes.\n\nThere was missing lock around tc_count increment inside\nsmb2_find_smb_sess_tcon_unlocked()."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"92d197ef7e9bb4994dae2bb17c2f19fa09d219a2","status":"affected","lessThan":"7585d4242f59185b084957fa077396e53dbf7c24","versionType":"git"},{"version":"953953abb66e52c224057ab91e404284fefeab62","status":"affected","lessThan":"7df1df6f40c0720d30206aa35c0343b962350e0d","versionType":"git"},{"version":"601dd3b79769b38d30b693c40afdb2a4b7edf9d0","status":"affected","lessThan":"13fb413ae22a37c69341918a6d651d19a9b0b9b7","versionType":"git"},{"version":"3969db6b22e3d90d8c5f22ac1a7fe0350a94c136","status":"affected","lessThan":"bf4ebdb19ff9b3cdf992b50715fe61633327416a","versionType":"git"},{"version":"96c4af418586ee9a6aab61738644366426e05316","status":"affected","lessThan":"e374f4e496fef8168784f93a4477d67be34485fd","versionType":"git"},{"version":"96c4af418586ee9a6aab61738644366426e05316","status":"affected","lessThan":"4d8690dace005a38e6dbde9ecce2da3ad85c7c41","versionType":"git"},{"version":"8c59eeeeffa1524ef57e173a89a1a3ff539888d5","status":"affected","versionType":"git"},{"version":"6.6.128","status":"affected","lessThan":"6.6.142","versionType":"semver"},{"version":"6.12.75","status":"affected","lessThan":"6.12.92","versionType":"semver"},{"version":"6.18.16","status":"affected","lessThan":"6.18.34","versionType":"semver"},{"version":"6.19.6","status":"affected","lessThan":"6.20","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/client/smb2transport.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.0","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.0","versionType":"semver"},{"version":"6.6.142","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.92","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.34","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.11","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/client/smb2transport.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/7585d4242f59185b084957fa077396e53dbf7c24"},{"url":"https://git.kernel.org/stable/c/7df1df6f40c0720d30206aa35c0343b962350e0d"},{"url":"https://git.kernel.org/stable/c/13fb413ae22a37c69341918a6d651d19a9b0b9b7"},{"url":"https://git.kernel.org/stable/c/bf4ebdb19ff9b3cdf992b50715fe61633327416a"},{"url":"https://git.kernel.org/stable/c/e374f4e496fef8168784f93a4477d67be34485fd"},{"url":"https://git.kernel.org/stable/c/4d8690dace005a38e6dbde9ecce2da3ad85c7c41"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - The flaw is in the in-kernel SMB/CIFS client (fs/smb/client/), reached when processing SMB2 responses received over TCP from a remote server in cifs_demultiplex_thread(). A network-positioned attacker controlling or impersonating the SMB server can drive the vulnerable cancelled-mid handling path.\nAC:L - The attacker controls SMB response timing and can trigger concurrent cifs_put_tcon() via server-initiated disconnect/reconnect, racing the unprotected tc_count increment. Cancelled-mid conditions arise from normal concurrent I/O, signals, and unmount/reconnect activity that the attacker can reliably provoke.\nPR:N - Exploitation requires no local privileges on the victim; a remote malicious or compromised SMB server can attack any client that has an active CIFS mount/session, without the attacker holding an account or capabilities on the victim host.\nUI:N - No victim interaction is needed at exploit time in common deployments where CIFS shares are automounted at boot or persistently connected (cloud file shares, enterprise NAS); the attacker abuses an already-established SMB session rather than requiring a new mount action.\nS:U - Impact is kernel memory corruption and potential local privilege escalation within the same kernel security domain, not a cross-boundary escape such as guest-to-host VM breakout.\nC:H - The race can cause a use-after-free of struct cifs_tcon; UAF of kernel heap objects enables arbitrary memory disclosure through controlled reuse of the freed structure.\nI:H - The UAF leads to subsequent kernel operations (SMB2_close, workqueue handlers) on freed memory, providing a path to arbitrary kernel write and potential code execution via heap grooming.\nA:H - Winning the refcount race causes use-after-free of cifs_tcon with continued kernel use of the freed object, which can trigger kernel oops/panic and denial of service even before full exploitation."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:27:35.201Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6.128","versionEndExcluding":"6.6.142"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12.75","versionEndExcluding":"6.12.92"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18.16","versionEndExcluding":"6.18.34"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.0","versionEndExcluding":"7.0.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.0","versionEndExcluding":"7.1"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.19.6"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-64136","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:36:58.919141Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-362","lang":"en","type":"CWE","description":"CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T20:28:13.962Z"}}]}}}