GHSA-5WW2-XM4X-3HM3
Vulnerability from github – Published: 2026-05-01 15:30 – Updated: 2026-05-03 09:33In the Linux kernel, the following vulnerability has been resolved:
ksmbd: validate response sizes in ipc_validate_msg()
ipc_validate_msg() computes the expected message size for each response type by adding (or multiplying) attacker-controlled fields from the daemon response to a fixed struct size in unsigned int arithmetic. Three cases can overflow:
KSMBD_EVENT_RPC_REQUEST: msg_sz = sizeof(struct ksmbd_rpc_command) + resp->payload_sz; KSMBD_EVENT_SHARE_CONFIG_REQUEST: msg_sz = sizeof(struct ksmbd_share_config_response) + resp->payload_sz; KSMBD_EVENT_LOGIN_REQUEST_EXT: msg_sz = sizeof(struct ksmbd_login_response_ext) + resp->ngroups * sizeof(gid_t);
resp->payload_sz is __u32 and resp->ngroups is __s32. Each addition can wrap in unsigned int; the multiplication by sizeof(gid_t) mixes signed and size_t, so a negative ngroups is converted to SIZE_MAX before the multiply. A wrapped value of msg_sz that happens to equal entry->msg_sz bypasses the size check on the next line, and downstream consumers (smb2pdu.c:6742 memcpy using rpc_resp->payload_sz, kmemdup in ksmbd_alloc_user using resp_ext->ngroups) then trust the unverified length.
Use check_add_overflow() on the RPC_REQUEST and SHARE_CONFIG_REQUEST paths to detect integer overflow without constraining functional payload size; userspace ksmbd-tools grows NDR responses in 4096-byte chunks for calls like NetShareEnumAll, so a hard transport cap is unworkable on the response side. For LOGIN_REQUEST_EXT, reject resp->ngroups outside the signed [0, NGROUPS_MAX] range up front and report the error from ipc_validate_msg() so it fires at the IPC boundary; with that bound the subsequent multiplication and addition stay well below UINT_MAX. The now-redundant ngroups check and pr_err in ksmbd_alloc_user() are removed.
This is the response-side analogue of aab98e2dbd64 ("ksmbd: fix integer overflows on 32 bit systems"), which hardened the request side.
{
"affected": [],
"aliases": [
"CVE-2026-31707"
],
"database_specific": {
"cwe_ids": [
"CWE-787"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-05-01T14:16:20Z",
"severity": "HIGH"
},
"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.",
"id": "GHSA-5ww2-xm4x-3hm3",
"modified": "2026-05-03T09:33:09Z",
"published": "2026-05-01T15:30:33Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31707"
},
{
"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/d6a6aa81eac2c9bff66dc6e191179cb69a14426b"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
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Nomenclature
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- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.