{ "schemaVersion": 1, "attribution": [ { "source": "CISA Known Exploited Vulnerabilities", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog", "licence": "US government work" }, { "source": "GitHub Advisory Database", "url": "https://github.com/advisories", "licence": "CC BY 4.0" }, { "source": "Have I Been Pwned", "url": "https://haveibeenpwned.com/", "licence": "CC BY 4.0" }, { "source": "CVE Program (CVE records)", "url": "https://www.cve.org/Legal/TermsOfUse", "licence": "CVE Terms of Use", "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.", "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." }, { "source": "FIRST EPSS", "url": "https://www.first.org/epss/", "licence": "free to use; FIRST requests attribution" } ], "record": { "id": "CVE-2025-40040", "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2025-40040", "idYear": 2025, "status": "PUBLISHED", "publishedAt": "2025-10-28T11:48:20.395Z", "updatedAt": "2026-10-15T22:02:36.606Z", "importedAt": "2026-10-24T01:57:34.152Z", "snapshot": { "id": "cve_2026-10-24_midnight_baseline", "at": "2026-10-24T00:00:00.000Z", "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z" }, "facts": { "title": "mm/ksm: fix flag-dropping behavior in ksm_madvise", "summary": "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\n\n[ 44.617726] Call Trace:\n[ 44.617926] \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]", "affected": [ { "vendor": "Linux", "product": "Linux", "defaultStatus": "unaffected", "versions": [ { "version": "63c17fb8e5a46a16e10e82005748837fd11a2024", "status": "affected", "versionType": "git", "lessThan": "850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71" }, { "version": "63c17fb8e5a46a16e10e82005748837fd11a2024", "status": "affected", "versionType": "git", "lessThan": "788e5385d0ff69cdba1cabccb9dab8d9647b9239" }, { "version": "63c17fb8e5a46a16e10e82005748837fd11a2024", "status": "affected", "versionType": "git", "lessThan": "b69f19244c2b6475c8a6eb72f0fb0d53509e48cd" }, { "version": "63c17fb8e5a46a16e10e82005748837fd11a2024", "status": "affected", "versionType": "git", "lessThan": "41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693" }, { "version": "63c17fb8e5a46a16e10e82005748837fd11a2024", "status": "affected", "versionType": "git", "lessThan": "92b82e232b8d8b116ac6e57aeae7a6033db92c60" }, { "version": "63c17fb8e5a46a16e10e82005748837fd11a2024", "status": "affected", "versionType": "git", "lessThan": "ac50c6e0a8f91a02b681af81abb2362fbb67cc18" }, { "version": "63c17fb8e5a46a16e10e82005748837fd11a2024", "status": "affected", "versionType": "git", "lessThan": "76385629f45740b7888f8fcd83bde955b10f61fe" }, { "version": "63c17fb8e5a46a16e10e82005748837fd11a2024", "status": "affected", "versionType": "git", "lessThan": "f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93" } ] }, { "vendor": "Linux", "product": "Linux", "defaultStatus": "affected", "versions": [ { "version": "4.6", "status": "affected" }, { "version": "0", "status": "unaffected", "versionType": "semver", "lessThan": "4.6" }, { "version": "5.4.302", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.4.*" }, { "version": "5.10.247", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.10.*" }, { "version": "5.15.197", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.15.*" }, { "version": "6.1.158", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.1.*" }, { "version": "6.6.114", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.6.*" }, { "version": "6.12.55", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.12.*" }, { "version": "6.17.3", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.17.*" }, { "version": "6.18", "status": "unaffected", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*" } ] } ] } } }