{"id":"CVE-2026-31707","summary":"ksmbd: validate response sizes in ipc_validate_msg()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: validate response sizes in ipc_validate_msg()\n\nipc_validate_msg() computes the expected message size for each\nresponse type by adding (or multiplying) attacker-controlled fields\nfrom the daemon response to a fixed struct size in unsigned int\narithmetic.  Three cases can overflow:\n\n  KSMBD_EVENT_RPC_REQUEST:\n      msg_sz = sizeof(struct ksmbd_rpc_command) + resp-\u003epayload_sz;\n  KSMBD_EVENT_SHARE_CONFIG_REQUEST:\n      msg_sz = sizeof(struct ksmbd_share_config_response) +\n               resp-\u003epayload_sz;\n  KSMBD_EVENT_LOGIN_REQUEST_EXT:\n      msg_sz = sizeof(struct ksmbd_login_response_ext) +\n               resp-\u003engroups * sizeof(gid_t);\n\nresp-\u003epayload_sz is __u32 and resp-\u003engroups is __s32.  Each addition\ncan wrap in unsigned int; the multiplication by sizeof(gid_t) mixes\nsigned and size_t, so a negative ngroups is converted to SIZE_MAX\nbefore the multiply.  A wrapped value of msg_sz that happens to\nequal entry-\u003emsg_sz bypasses the size check on the next line, and\ndownstream consumers (smb2pdu.c:6742 memcpy using rpc_resp-\u003epayload_sz,\nkmemdup in ksmbd_alloc_user using resp_ext-\u003engroups) then trust the\nunverified length.\n\nUse check_add_overflow() on the RPC_REQUEST and SHARE_CONFIG_REQUEST\npaths to detect integer overflow without constraining functional\npayload size; userspace ksmbd-tools grows NDR responses in 4096-byte\nchunks for calls like NetShareEnumAll, so a hard transport cap is\nunworkable on the response side.  For LOGIN_REQUEST_EXT, reject\nresp-\u003engroups outside the signed [0, NGROUPS_MAX] range up front and\nreport the error from ipc_validate_msg() so it fires at the IPC\nboundary; with that bound the subsequent multiplication and addition\nstay well below UINT_MAX.  The now-redundant ngroups check and\npr_err in ksmbd_alloc_user() are removed.\n\nThis is the response-side analogue of aab98e2dbd64 (\"ksmbd: fix\ninteger overflows on 32 bit systems\"), which hardened the request\nside.","modified":"2026-06-18T03:56:13.275386391Z","published":"2026-05-01T13:56:05.219Z","related":["CGA-ghjw-8qpc-p3rh","openSUSE-SU-2026:10793-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31707.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/299db777ea0cfa5c407e41b045c24a14c034c27b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7dd0c858e1909769a4c91842724315ee74f1a5f1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/99c631d0366c1eab8fb188fe66425f4581ebdde4"},{"type":"WEB","url":"https://git.kernel.org/stable/c/bf396208418371174869baba9434535cd3288e80"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d6a6aa81eac2c9bff66dc6e191179cb69a14426b"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31707.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31707"},{"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":"0626e6641f6b467447c81dd7678a69c66f7746cf"},{"fixed":"bf396208418371174869baba9434535cd3288e80"},{"fixed":"7dd0c858e1909769a4c91842724315ee74f1a5f1"},{"fixed":"299db777ea0cfa5c407e41b045c24a14c034c27b"},{"fixed":"99c631d0366c1eab8fb188fe66425f4581ebdde4"},{"fixed":"d6a6aa81eac2c9bff66dc6e191179cb69a14426b"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31707.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.15.0"},{"fixed":"6.6.141"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.84"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.25"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.0.2"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31707.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H"}]}