{"id":"CVE-2025-40040","revision":null,"records":[{"revision":"6dedc961624948a3830551816bc7283f","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2025-40040","aliases":[],"title":"mm/ksm: fix flag-dropping behavior in ksm_madvise","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/ksm: fix flag-dropping behavior in ksm_madvise\n\nsyzkaller discovered the following crash: (kernel BUG)\n\n[   44.607039] ------------[ cut here ]------------\n[   44.607422] kernel BUG at mm/userfaultfd.c:2067!\n[   44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI\n[   44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none)\n[   44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014\n[   44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460\n\n<snip other registers, drop unreliable trace>\n\n[   44.617726] Call Trace:\n[   44.617926]  <TASK>\n[   44.619284]  userfaultfd_release+0xef/0x1b0\n[   44.620976]  __fput+0x3f9/0xb60\n[   44.621240]  fput_close_sync+0x110/0x210\n[   44.622222]  __x64_sys_close+0x8f/0x120\n[   44.622530]  do_syscall_64+0x5b/0x2f0\n[   44.622840]  entry_SYSCALL_64_after_hwframe+0x76/0x7e\n[   44.623244] RIP: 0033:0x7f365bb3f227\n\nKernel panics because it detects UFFD inconsistency during\nuserfaultfd_release_all().  Specifically, a VMA which has a valid pointer\nto vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags.\n\nThe inconsistency is caused in ksm_madvise(): when user calls madvise()\nwith MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode,\nit accidentally clears all flags stored in the upper 32 bits of\nvma->vm_flags.\n\nAssuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and\nint are 32-bit wide.  This setup causes the following mishap during the &=\n~VM_MERGEABLE assignment.\n\nVM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000'0000. \nAfter ~ is applied, it becomes 0x7fff'ffff unsigned int, which is then\npromoted to unsigned long before the & operation.  This promotion fills\nupper 32 bits with leading 0s, as we're doing unsigned conversion (and\neven for a signed conversion, this wouldn't help as the leading bit is 0).\n& operation thus ends up AND-ing vm_flags with 0x0000'0000'7fff'ffff\ninstead of intended 0xffff'ffff'7fff'ffff and hence accidentally clears\nthe upper 32-bits of its value.\n\nFix it by changing `VM_MERGEABLE` constant to unsigned long, using the\nBIT() macro.\n\nNote: other VM_* flags are not affected: This only happens to the\nVM_MERGEABLE flag, as the other VM_* flags are all constants of type int\nand after ~ operation, they end up with leading 1 and are thus converted\nto unsigned long with leading 1s.\n\nNote 2:\nAfter commit 31defc3b01d9 (\"userfaultfd: remove (VM_)BUG_ON()s\"), this is\nno longer a kernel BUG, but a WARNING at the same place:\n\n[   45.595973] WARNING: CPU: 1 PID: 2474 at mm/userfaultfd.c:2067\n\nbut the root-cause (flag-drop) remains the same.\n\n[akpm@linux-foundation.org: rust bindgen wasn't able to handle BIT(), from Miguel]","state":0,"publishedAt":"2025-10-28T11:48:20.395+00:00","modifiedAt":"2026-10-15T22:02:36.606+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"include/linux/mm.h\",\n                        \"rust/bindings/bindings_helper.h\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"63c17fb8e5a46a16e10e82005748837fd11a2024\",\n                            \"lessThan\": \"850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"63c17fb8e5a46a16e10e82005748837fd11a2024\",\n                            \"lessThan\": \"788e5385d0ff69cdba1cabccb9dab8d9647b9239\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"63c17fb8e5a46a16e10e82005748837fd11a2024\",\n                            \"lessThan\": \"b69f19244c2b6475c8a6eb72f0fb0d53509e48cd\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"63c17fb8e5a46a16e10e82005748837fd11a2024\",\n                            \"lessThan\": \"41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"63c17fb8e5a46a16e10e82005748837fd11a2024\",\n                            \"lessThan\": \"92b82e232b8d8b116ac6e57aeae7a6033db92c60\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"63c17fb8e5a46a16e10e82005748837fd11a2024\",\n                            \"lessThan\": \"ac50c6e0a8f91a02b681af81abb2362fbb67cc18\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"63c17fb8e5a46a16e10e82005748837fd11a2024\",\n                            \"lessThan\": \"76385629f45740b7888f8fcd83bde955b10f61fe\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"63c17fb8e5a46a16e10e82005748837fd11a2024\",\n                            \"lessThan\": \"f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"include/linux/mm.h\",\n                        \"rust/bindings/bindings_helper.h\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"4.6\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"4.6\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.4.302\",\n                            \"lessThanOrEqual\": \"5.4.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.10.247\",\n                            \"lessThanOrEqual\": \"5.10.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.15.197\",\n                            \"lessThanOrEqual\": \"5.15.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.1.158\",\n                            \"lessThanOrEqual\": \"6.1.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.6.114\",\n                            \"lessThanOrEqual\": \"6.6.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.12.55\",\n                            \"lessThanOrEqual\": \"6.12.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.17.3\",\n                            \"lessThanOrEqual\": \"6.17.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8,"severity":"HIGH"}],"references":["https://git.kernel.org/stable/c/850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71","https://git.kernel.org/stable/c/788e5385d0ff69cdba1cabccb9dab8d9647b9239","https://git.kernel.org/stable/c/b69f19244c2b6475c8a6eb72f0fb0d53509e48cd","https://git.kernel.org/stable/c/41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693","https://git.kernel.org/stable/c/92b82e232b8d8b116ac6e57aeae7a6033db92c60","https://git.kernel.org/stable/c/ac50c6e0a8f91a02b681af81abb2362fbb67cc18","https://git.kernel.org/stable/c/76385629f45740b7888f8fcd83bde955b10f61fe","https://git.kernel.org/stable/c/f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2025-40040","license":"CVE Program Terms of Use","key":"cve-program:CVE-2025-40040","identifiers":["CVE-2025-40040"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all 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Not a global EUVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. No reader inventory is sent.","generation":"enrichment-469e0902b40147e98a6498cf72d41be8","complete":true,"records":13655,"lastAttemptAt":"2026-11-09T12:14:17.3321495+00:00","lastSuccessAt":"2026-11-09T12:14:17.327+00:00","error":null,"lastVerifiedAt":"2026-11-09T12:14:17.327+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":13707,"expectedIdentifiers":13707,"failedIdentifiers":0},{"source":"first-epss:nuget","scope":"FIRST EPSS for explicit CVE aliases in the collected public NuGet archive. Not a global EPSS backfill.","generation":"2026-11-09T12:02:21.9910047+00:00","complete":true,"records":1096,"lastAttemptAt":"2026-11-09T12:02:21.9910047+00:00","lastSuccessAt":"2026-11-09T12:02:22.1781502+00:00","error":null,"lastVerifiedAt":"2026-11-09T12:02:22.1781508+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"nvd","scope":"Rolling NVD lookups of CVE aliases in current public OSV archives; 500 identifiers per refresh, rechecked after 48 hours. Not a global NVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. 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