{"id":"CVE-2026-89637","title":"smb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2","summary":"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, mi…","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","cwe":["CWE-825"],"vendor":"Linux","product":"Linux","affected":["Linux >= 316cf94a910f6f93d43cc574359d163ccae098a3 < 9eed72e9534b10a6d9f8f5146feff3db53aebdba","Linux >= 316cf94a910f6f93d43cc574359d163ccae098a3 < 5e6533a683f6a851158d9f33fb4ea8f4f25d7f84","Linux >= 316cf94a910f6f93d43cc574359d163ccae098a3 < 730d0bb19507b9e19c2fe5343109ac618e2fbce5","Linux 3.6"],"published":"2026-09-11","updated":"2026-10-19","sourceUpdated":"2026-10-19T08:50:09.230Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-89637","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"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89637.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-89637"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2532405"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89637"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89637"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89637.mbox"}],"tags":["cve.org","csaf","vex","red-hat","score-dispute"],"epss":0.00597,"epssPercentile":0.48352,"scores":{"cna":9.8,"vendor":7},"ingestedAt":"2026-09-14T15:23:07.476Z","slug":"CVE-2026-89637","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `Linux >= 316cf94a910f6f93d43cc574359d163ccae098a3 < 9eed72e9534b10a6d9f8f5146feff3db53aebdba`\n- `Linux >= 316cf94a910f6f93d43cc574359d163ccae098a3 < 5e6533a683f6a851158d9f33fb4ea8f4f25d7f84`\n- `Linux >= 316cf94a910f6f93d43cc574359d163ccae098a3 < 730d0bb19507b9e19c2fe5343109ac618e2fbce5`\n- `Linux 3.6`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-18 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89637.json)","depth":"midnight","depthScore":54,"depthScoreParts":{"impact":53.9,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":224651,"id":"CVE-2026-89637","ts":1792401458640,"field":"cvss","old":"7","new":"9.8"},{"seq":224650,"id":"CVE-2026-89637","ts":1792401458640,"field":"severity","old":"high","new":"critical"},{"seq":206926,"id":"CVE-2026-89637","ts":1789749703101,"field":"cvss","old":"7.1","new":"7"},{"seq":203007,"id":"CVE-2026-89637","ts":1789403733324,"field":"cvss","old":"9.8","new":"7.1"},{"seq":203006,"id":"CVE-2026-89637","ts":1789403733324,"field":"severity","old":"critical","new":"high"},{"seq":197817,"id":"CVE-2026-89637","ts":1789384320524,"field":"cvss","old":"7.1","new":"9.8"},{"seq":197816,"id":"CVE-2026-89637","ts":1789384320524,"field":"severity","old":"high","new":"critical"},{"seq":183762,"id":"CVE-2026-89637","ts":1789356677280,"field":"cvss","old":"9.8","new":"7.1"},{"seq":183761,"id":"CVE-2026-89637","ts":1789356677280,"field":"severity","old":"critical","new":"high"},{"seq":153478,"id":"CVE-2026-89637","ts":1789285350678,"field":"cvss","old":null,"new":"9.8"},{"seq":153477,"id":"CVE-2026-89637","ts":1789285350678,"field":"severity","old":"none","new":"critical"},{"seq":147257,"id":"CVE-2026-89637","ts":1789270204938,"field":"cvss","old":null,"new":"7.1"},{"seq":147256,"id":"CVE-2026-89637","ts":1789270204938,"field":"severity","old":"none","new":"high"},{"seq":109004,"id":"CVE-2026-89637","ts":1789183729916,"field":"cvss","old":null,"new":"7.1"},{"seq":109003,"id":"CVE-2026-89637","ts":1789183729916,"field":"severity","old":"none","new":"high"}]}