{"id":"CVE-2026-89637","summary":"smb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2","details":"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-\u003eresp_buf\nset, mid-\u003emultiRsp 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-\u003eresp_buf with the new buffer (leaking the\nprimary buffer) and, because mid-\u003emultiRsp is set, skips the\nserver-\u003esmallbuf/bigbuf NULL-out.  When the user thread frees\nmid-\u003eresp_buf, server-\u003esmallbuf or server-\u003ebigbuf 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-\u003emultiRsp 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-\u003eresp_buf or the server buffer pointers.","modified":"2026-09-14T03:46:20.400331099Z","published":"2026-09-11T19:45:31.048Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89637.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/5e6533a683f6a851158d9f33fb4ea8f4f25d7f84"},{"type":"WEB","url":"https://git.kernel.org/stable/c/730d0bb19507b9e19c2fe5343109ac618e2fbce5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9eed72e9534b10a6d9f8f5146feff3db53aebdba"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89637.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89637"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"316cf94a910f6f93d43cc574359d163ccae098a3"},{"fixed":"9eed72e9534b10a6d9f8f5146feff3db53aebdba"},{"fixed":"5e6533a683f6a851158d9f33fb4ea8f4f25d7f84"},{"fixed":"730d0bb19507b9e19c2fe5343109ac618e2fbce5"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89637.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.6.0"},{"fixed":"6.18.51"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89637.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"}]}