{"id":"CVE-2026-31707","title":"ksmbd: validate response sizes in ipc_validate_msg()","summary":"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-c…","severity":"high","cvss":7.1,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < 52518503a1a00bc33e9522c4eb05df023e3ae978","Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < bf396208418371174869baba9434535cd3288e80","Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < 7dd0c858e1909769a4c91842724315ee74f1a5f1","Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < 299db777ea0cfa5c407e41b045c24a14c034c27b","Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < 99c631d0366c1eab8fb188fe66425f4581ebdde4","Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < d6a6aa81eac2c9bff66dc6e191179cb69a14426b","Linux 5.15"],"published":"2026-05-01","updated":"2026-10-30","sourceUpdated":"2026-10-30T12:24:35.243Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31707","references":[{"url":"https://git.kernel.org/stable/c/52518503a1a00bc33e9522c4eb05df023e3ae978"},{"url":"https://git.kernel.org/stable/c/bf396208418371174869baba9434535cd3288e80"},{"url":"https://git.kernel.org/stable/c/7dd0c858e1909769a4c91842724315ee74f1a5f1"},{"url":"https://git.kernel.org/stable/c/299db777ea0cfa5c407e41b045c24a14c034c27b"},{"url":"https://git.kernel.org/stable/c/99c631d0366c1eab8fb188fe66425f4581ebdde4"},{"url":"https://git.kernel.org/stable/c/d6a6aa81eac2c9bff66dc6e191179cb69a14426b"}],"tags":["cve.org"],"epss":0.00125,"epssPercentile":0.02256,"ingestedAt":"2026-11-05T15:02:32.236Z","slug":"CVE-2026-31707","body":"## Overview\n\nIn 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->payload_sz;\n  KSMBD_EVENT_SHARE_CONFIG_REQUEST:\n      msg_sz = sizeof(struct ksmbd_share_config_response) +\n               resp->payload_sz;\n  KSMBD_EVENT_LOGIN_REQUEST_EXT:\n      msg_sz = sizeof(struct ksmbd_login_response_ext) +\n               resp->ngroups * sizeof(gid_t);\n\nresp->payload_sz is __u32 and resp->ngroups 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->msg_sz bypasses the size check on the next line, and\ndownstream consumers (smb2pdu.c:6742 memcpy using rpc_resp->payload_sz,\nkmemdup in ksmbd_alloc_user using resp_ext->ngroups) 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->ngroups 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.\n\n## Affected\n\n- `Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < 52518503a1a00bc33e9522c4eb05df023e3ae978`\n- `Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < bf396208418371174869baba9434535cd3288e80`\n- `Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < 7dd0c858e1909769a4c91842724315ee74f1a5f1`\n- `Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < 299db777ea0cfa5c407e41b045c24a14c034c27b`\n- `Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < 99c631d0366c1eab8fb188fe66425f4581ebdde4`\n- `Linux >= 0626e6641f6b467447c81dd7678a69c66f7746cf < d6a6aa81eac2c9bff66dc6e191179cb69a14426b`\n- `Linux 5.15`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":39,"depthScoreParts":{"impact":39.1,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}