{"id":"CVE-2026-89630","state":"PUBLISHED","title":"smb: client: restore the data_offset bound in is_valid_oplock_break()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: restore the data_offset bound in is_valid_oplock_break()\n\nCommit 83bfbd0bb902 (\"cifs: Remove the RFC1002 header from smb_hdr\")\nchanged the quantity this bound is measured against.  It used to be\nsrv->total_read minus the 4-byte RFC1002 preamble that total_read then\nincluded, so it was the SMB message length.  The same commit stopped\ncounting the preamble, and the mechanical substitution to\nsrv->total_read - srv->pdu_size left an expression that is identically\nzero: standard_receive3() reads MID_HEADER_SIZE() bytes and then exactly\npdu_length - MID_HEADER_SIZE() more, adding both to total_read.\n\nlen is therefore 0, the subtraction below it wraps, and no __u32\nDataOffset can exceed the result, so the check from commit 097f5863b1a0\n(\"cifs: read overflow in is_valid_oplock_break()\") no longer rejects\nanything.  Use total_read, which is now the message length on its own.","publishedAt":"2026-09-11T19:45:25.697Z","updatedAt":"2026-10-19T08:50:02.437Z","severity":{"score":9.1,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"83bfbd0bb9025f98fa62b44f93bd67466773d1db","status":"affected","lessThan":"5b16a1967a01ad4496a7206a87c3eb16f1df2b05","versionType":"git"},{"version":"83bfbd0bb9025f98fa62b44f93bd67466773d1db","status":"affected","lessThan":"ba22f575de9deeae4ae0859ca4315a7698226237","versionType":"git"},{"version":"78e718c5aa146063cd70d2cc68297c3ac41f31ee","status":"affected","versionType":"git"},{"version":"6.18.56","status":"affected","lessThan":"6.19","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/client/smb1misc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.19","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","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/smb1misc.c"]}],"references":["https://git.kernel.org/stable/c/5b16a1967a01ad4496a7206a87c3eb16f1df2b05","https://git.kernel.org/stable/c/ba22f575de9deeae4ae0859ca4315a7698226237"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89630.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89630","state":"PUBLISHED","datePublished":"2026-09-11T19:45:25.697Z","dateUpdated":"2026-10-19T08:50:02.437Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.738Z"},"containers":{"cna":{"title":"smb: client: restore the data_offset bound in is_valid_oplock_break()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: restore the data_offset bound in is_valid_oplock_break()\n\nCommit 83bfbd0bb902 (\"cifs: Remove the RFC1002 header from smb_hdr\")\nchanged the quantity this bound is measured against.  It used to be\nsrv->total_read minus the 4-byte RFC1002 preamble that total_read then\nincluded, so it was the SMB message length.  The same commit stopped\ncounting the preamble, and the mechanical substitution to\nsrv->total_read - srv->pdu_size left an expression that is identically\nzero: standard_receive3() reads MID_HEADER_SIZE() bytes and then exactly\npdu_length - MID_HEADER_SIZE() more, adding both to total_read.\n\nlen is therefore 0, the subtraction below it wraps, and no __u32\nDataOffset can exceed the result, so the check from commit 097f5863b1a0\n(\"cifs: read overflow in is_valid_oplock_break()\") no longer rejects\nanything.  Use total_read, which is now the message length on its own."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"83bfbd0bb9025f98fa62b44f93bd67466773d1db","status":"affected","lessThan":"5b16a1967a01ad4496a7206a87c3eb16f1df2b05","versionType":"git"},{"version":"83bfbd0bb9025f98fa62b44f93bd67466773d1db","status":"affected","lessThan":"ba22f575de9deeae4ae0859ca4315a7698226237","versionType":"git"},{"version":"78e718c5aa146063cd70d2cc68297c3ac41f31ee","status":"affected","versionType":"git"},{"version":"6.18.56","status":"affected","lessThan":"6.19","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/client/smb1misc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.19","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","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/smb1misc.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/5b16a1967a01ad4496a7206a87c3eb16f1df2b05"},{"url":"https://git.kernel.org/stable/c/ba22f575de9deeae4ae0859ca4315a7698226237"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H","baseScore":9.1,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - The flaw is in the in-kernel SMB1 client demultiplex path: a remote peer sends an unsolicited SMB_COM_NT_TRANSACT response over TCP/445 and cifs_demultiplex_thread() calls is_valid_oplock_break() on unmatched frames, so a malicious or compromised SMB server (or MITM) reaches it via network protocol data.\nAC:L - The attacker fully controls Command, Flags, ByteCount, and DataOffset in a single unsolicited frame; the broken bound wraps so any DataOffset is accepted and the resulting heap over-read is deterministic, with no race or condition the attacker cannot influence once the client is on the SMB1 connection.\nPR:N - A matching MID, session setup, or tree connect is not required: after negotiate, an unmatched NT_TRANSACT+RESPONSE frame is treated as an oplock/dnotify break before authentication, so the malicious server needs no credentials or privileges on the client host.\nUI:N - On a persistent SMB1 mount (cifsroot, automount, or an already-mounted legacy NAS share) the cifsd thread processes unsolicited frames after the existing connection or reconnect, so no additional victim action is required at attack time.\nS:U - The out-of-bounds/use-after-free read occurs in kernel heap used by the CIFS client on the same host kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - Attacker-controlled DataOffset displaces file_notify_information into adjacent or freed cifs_small_rq slab objects (KASAN use-after-free read), and printing FileName with %s can walk unbounded kernel memory, so the disclosure is not limited to a few bounded bytes.\nI:N - The displaced pointer is only read (Action and FileName for a debug print); the bug does not write through that pointer or otherwise provide a kernel memory-modification or control-flow primitive.\nA:H - The KASAN-confirmed slab use-after-free and unmapped over-read run in the cifsd demultiplex thread and can oops or panic the kernel, and a malicious peer can repeat the unsolicited frame to retrigger the crash."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:50:02.437Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.19","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.19","versionEndExcluding":"7.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18.56"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}