CVE-2026-89637

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-89637", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.739Z", "datePublished": "2026-09-11T19:45:31.048Z", "dateUpdated": "2026-10-19T08:50:09.230Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:50:09.230Z"}, "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": {"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 - 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."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/smb/client/smb1transport.c"], "versions": [{"version": "316cf94a910f6f93d43cc574359d163ccae098a3", "lessThan": "9eed72e9534b10a6d9f8f5146feff3db53aebdba", "status": "affected", "versionType": "git"}, {"version": "316cf94a910f6f93d43cc574359d163ccae098a3", "lessThan": "5e6533a683f6a851158d9f33fb4ea8f4f25d7f84", "status": "affected", "versionType": "git"}, {"version": "316cf94a910f6f93d43cc574359d163ccae098a3", "lessThan": "730d0bb19507b9e19c2fe5343109ac618e2fbce5", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/smb/client/smb1transport.c"], "versions": [{"version": "3.6", "status": "affected"}, {"version": "0", "lessThan": "3.6", "status": "unaffected", "versionType": "semver"}, {"version": "6.18.51", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.2.4", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.6", "versionEndExcluding": "6.18.51"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.6", "versionEndExcluding": "7.2.4"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.6", "versionEndExcluding": "7.3"}]}]}], "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"}}}}

{}

{"affected": [{"affectedData": [{"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"}]}], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "cveTags": [], "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."}], "id": "CVE-2026-89637", "lastModified": "2026-10-19T09:18:00.780", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 9.8, "baseSeverity": "CRITICAL", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 5.9, "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary"}]}, "published": "2026-09-11T20:19:49.370", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/5e6533a683f6a851158d9f33fb4ea8f4f25d7f84"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/730d0bb19507b9e19c2fe5343109ac618e2fbce5"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/9eed72e9534b10a6d9f8f5146feff3db53aebdba"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Received"}

{"bugzilla": {"description": "kernel: Kernel: Use-After-Free vulnerability in SMB client due to malformed TRANSACT2 response", "id": "2532405", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2532405"}, "csaw": false, "cvss3": {"cvss3_base_score": "7.1", "cvss3_scoring_vector": "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H", "status": "draft"}, "cwe": "CWE-825", "details": ["A flaw was found in the Linux kernel's Server Message Block (SMB) client. When processing a malformed secondary TRANSACT2 response, a use-after-free (UAF) vulnerability and a buffer leak can occur in the `cifs_check_trans2()` function. This can lead to a dangling buffer being reused by the demux thread, potentially allowing an attacker to achieve arbitrary code execution or cause a denial of service."], "name": "CVE-2026-89637", "public_date": "2026-09-11T19:45:31Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-89637\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-89637\nhttps://git.kernel.org/stable/c/5e6533a683f6a851158d9f33fb4ea8f4f25d7f84\nhttps://git.kernel.org/stable/c/730d0bb19507b9e19c2fe5343109ac618e2fbce5\nhttps://git.kernel.org/stable/c/9eed72e9534b10a6d9f8f5146feff3db53aebdba"], "threat_severity": "Important"}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[316cf94a910f6f93d43cc574359d163ccae098a3,9eed72e9534b10a6d9f8f5146feff3db53aebdba)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[316cf94a910f6f93d43cc574359d163ccae098a3,5e6533a683f6a851158d9f33fb4ea8f4f25d7f84)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[316cf94a910f6f93d43cc574359d163ccae098a3,730d0bb19507b9e19c2fe5343109ac618e2fbce5)"}}], "enrichment": {"confidence": 99.0, "confidence_source": "inferred", "scores": [{"score": 99.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "3.6"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[0,3.6)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[6.18.51,6.19.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[7.2.4,7.3.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[7.3-rc1,*]"}}], "enrichment": {"confidence": 99.0, "confidence_source": "inferred", "scores": [{"score": 99.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}], "created": "2026-09-12T09:15:12.757345+00:00", "updated": "2026-09-15T21:15:14.618885+00:00", "vendors": ["linux", "linux$PRODUCT$linux_kernel"]}