{"api_version":"1","generated_at":"2026-10-27T04:32:00+00:00","cve":"CVE-2026-89637","urls":{"html":"https://cve.report/CVE-2026-89637","api":"https://cve.report/api/cve/CVE-2026-89637.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-89637","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-89637"},"summary":{"title":"smb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2\n\nWhen a valid primary TRANSACT2 response has been received (mid->resp_buf\nset, mid->multiRsp true) and a subsequent secondary response causes\ncifs_check_trans2() to return false -- either because the SMB header is\ninvalid (malformed != 0) or because check2ndT2() rejects the PDU --\nhandle_mid() overwrites mid->resp_buf with the new buffer (leaking the\nprimary buffer) and, because mid->multiRsp is set, skips the\nserver->smallbuf/bigbuf NULL-out.  When the user thread frees\nmid->resp_buf, server->smallbuf or server->bigbuf is left dangling; the\ndemux thread reuses it for the next packet, resulting in a use-after-free.\n\nCombine both early-exit conditions and, when mid->multiRsp is already\nset, abort the pending transaction inline: set multiEnd, call\ndequeue_mid() with malformed=true, and return true so handle_mid() exits\nwithout touching mid->resp_buf or the server buffer pointers.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-09-11 20:19:49","updated_at":"2026-10-19 09:18:00"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"9.8","severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","data":{"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","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"9.8","severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","data":{"baseScore":9.8,"baseSeverity":"CRITICAL","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"references":[{"url":"https://git.kernel.org/stable/c/5e6533a683f6a851158d9f33fb4ea8f4f25d7f84","name":"https://git.kernel.org/stable/c/5e6533a683f6a851158d9f33fb4ea8f4f25d7f84","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/9eed72e9534b10a6d9f8f5146feff3db53aebdba","name":"https://git.kernel.org/stable/c/9eed72e9534b10a6d9f8f5146feff3db53aebdba","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/730d0bb19507b9e19c2fe5343109ac618e2fbce5","name":"https://git.kernel.org/stable/c/730d0bb19507b9e19c2fe5343109ac618e2fbce5","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89637","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89637","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 316cf94a910f6f93d43cc574359d163ccae098a3 9eed72e9534b10a6d9f8f5146feff3db53aebdba git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 316cf94a910f6f93d43cc574359d163ccae098a3 5e6533a683f6a851158d9f33fb4ea8f4f25d7f84 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 316cf94a910f6f93d43cc574359d163ccae098a3 730d0bb19507b9e19c2fe5343109ac618e2fbce5 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 3.6","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 3.6 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.51 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2.4 7.2.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.3 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"89637","cve":"CVE-2026-89637","epss":"0.005880000","percentile":"0.463170000","score_date":"2026-09-14","updated_at":"2026-09-15 00:00:42"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["fs/smb/client/smb1transport.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"9eed72e9534b10a6d9f8f5146feff3db53aebdba","status":"affected","version":"316cf94a910f6f93d43cc574359d163ccae098a3","versionType":"git"},{"lessThan":"5e6533a683f6a851158d9f33fb4ea8f4f25d7f84","status":"affected","version":"316cf94a910f6f93d43cc574359d163ccae098a3","versionType":"git"},{"lessThan":"730d0bb19507b9e19c2fe5343109ac618e2fbce5","status":"affected","version":"316cf94a910f6f93d43cc574359d163ccae098a3","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["fs/smb/client/smb1transport.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":"6.18.*","status":"unaffected","version":"6.18.51","versionType":"semver"},{"lessThanOrEqual":"7.2.*","status":"unaffected","version":"7.2.4","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.3","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.51","versionStartIncluding":"3.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2.4","versionStartIncluding":"3.6","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.3","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: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2\n\nWhen a valid primary TRANSACT2 response has been received (mid->resp_buf\nset, mid->multiRsp true) and a subsequent secondary response causes\ncifs_check_trans2() to return false -- either because the SMB header is\ninvalid (malformed != 0) or because check2ndT2() rejects the PDU --\nhandle_mid() overwrites mid->resp_buf with the new buffer (leaking the\nprimary buffer) and, because mid->multiRsp is set, skips the\nserver->smallbuf/bigbuf NULL-out.  When the user thread frees\nmid->resp_buf, server->smallbuf or server->bigbuf is left dangling; the\ndemux thread reuses it for the next packet, resulting in a use-after-free.\n\nCombine both early-exit conditions and, when mid->multiRsp is already\nset, abort the pending transaction inline: set multiEnd, call\ndequeue_mid() with malformed=true, and return true so handle_mid() exits\nwithout touching mid->resp_buf or the server buffer pointers."}],"metrics":[{"cvssV3_1":{"baseScore":9.8,"baseSeverity":"CRITICAL","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"},"scenarios":[{"lang":"en","value":"AV:N - cifs_check_trans2() runs in cifs_demultiplex_thread on SMB1 TRANS2 responses received over TCP/445; a malicious or compromised SMB1 server (or MITM on an unsigned session) delivers the crafted primary and malformed secondary PDUs entirely over the network.\nAC:L - The attacker fully controls both fragments: a valid primary with TotalDataCount greater than DataCount sets mid->multiRsp, then a secondary with WordCount != 10, inconsistent counts, or a malformed SMB header makes cifs_check_trans2() return false. The resulting UAF is deterministic with no race outside the attacker's control.\nPR:N - The attacker is the remote SMB peer and needs no account or privileges on the victim; cifs_check_trans2() runs in the demux thread on server-supplied frames, and session credentials belong to the client mount, not the attacking server.\nUI:N - Once an SMB1 CIFS mount exists (fstab, autofs, cifsroot, embedded/industrial NAS; CONFIG_CIFS_ALLOW_INSECURE_LEGACY defaults on), reconnect and ordinary lookup/readdir/getattr plus cifs_qfs_tcon QUERY_FS_INFO issue TRANS2 automatically, so the server can trigger the UAF with no further user action.\nS:U - The use-after-free corrupts the client kernel's own CIFS receive-buffer mempool (cifs_req_poolp/cifs_sm_req_poolp) within the same host security authority; this is not a VM escape, IOMMU bypass, or sandbox boundary crossing.\nC:H - handle_mid() overwrites mid->resp_buf without detaching server->bigbuf/smallbuf, so after the user thread frees the buffer the demux thread reuses the dangling mempool object for the next packet; that use-after-free enables heap reuse and arbitrary kernel memory disclosure.\nI:H - The same dangling server receive buffer is written by cifsd and later freed by the user thread, yielding a kernel heap use-after-free. Attacker-controlled subsequent SMB payloads and heap grooming can turn this into an arbitrary write or control-flow hijack.\nA:H - Reusing a freed CIFS small/large response buffer can fault on poisoned or unmapped slab objects and oops or panic the demux thread, and a malicious server can retrigger the primary-then-malformed-secondary sequence on every multi-part TRANS2."}]}],"providerMetadata":{"dateUpdated":"2026-10-19T08:50:09.230Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/9eed72e9534b10a6d9f8f5146feff3db53aebdba"},{"url":"https://git.kernel.org/stable/c/5e6533a683f6a851158d9f33fb4ea8f4f25d7f84"},{"url":"https://git.kernel.org/stable/c/730d0bb19507b9e19c2fe5343109ac618e2fbce5"}],"title":"smb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-89637","datePublished":"2026-09-11T19:45:31.048Z","dateReserved":"2026-09-11T19:38:34.739Z","dateUpdated":"2026-10-19T08:50:09.230Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-09-11 20:19:49","lastModifiedDate":"2026-10-19 09:18:00","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"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","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":3.9,"impactScore":5.9}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"89637","Ordinal":"1","Title":"smb: client: fix UAF and buffer leak in cifs_check_trans2() for ","CVE":"CVE-2026-89637","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"89637","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2\n\nWhen a valid primary TRANSACT2 response has been received (mid->resp_buf\nset, mid->multiRsp true) and a subsequent secondary response causes\ncifs_check_trans2() to return false -- either because the SMB header is\ninvalid (malformed != 0) or because check2ndT2() rejects the PDU --\nhandle_mid() overwrites mid->resp_buf with the new buffer (leaking the\nprimary buffer) and, because mid->multiRsp is set, skips the\nserver->smallbuf/bigbuf NULL-out.  When the user thread frees\nmid->resp_buf, server->smallbuf or server->bigbuf is left dangling; the\ndemux thread reuses it for the next packet, resulting in a use-after-free.\n\nCombine both early-exit conditions and, when mid->multiRsp is already\nset, abort the pending transaction inline: set multiEnd, call\ndequeue_mid() with malformed=true, and return true so handle_mid() exits\nwithout touching mid->resp_buf or the server buffer pointers.","Type":"Description","Title":"smb: client: fix UAF and buffer leak in cifs_check_trans2() for "}]}}}