300 lines
18 KiB
JSON
300 lines
18 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2025-40040",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2025-04-16T07:20:57.154Z",
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"datePublished": "2025-10-28T11:48:20.395Z",
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"dateUpdated": "2026-10-15T22:02:36.606Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-08-05T12:07:14.111Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"value": "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]"
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 7.8,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:L - The bug is reached purely through the madvise(2) syscall (MADV_MERGEABLE/MADV_UNMERGEABLE) on the caller's own address space, with no network or remote component. Local access to the system is required.\nAC:L - The flag drop is a deterministic C integer-promotion defect that triggers on every MADV_UNMERGEABLE call — no race, no memory-layout grooming, and no conditions outside the attacker's control. A short single-threaded reproducer (memfd + MAP_PRIVATE + MADV_MERGEABLE + UFFDIO_REGISTER(MINOR) + MADV_UNMERGEABLE + close) works 100% of the time.\nPR:L - Any unprivileged local user can do this: memfd_create() and MAP_PRIVATE need no capability, and userfaultfd(UFFD_USER_MODE_ONLY) is explicitly allowed to unprivileged callers regardless of vm.unprivileged_userfaultfd or CAP_SYS_PTRACE. The mseal/pkey/shadow-stack flag-drop variants need no special facility at all.\nUI:N - The attacking process performs the entire sequence itself via its own syscalls; no other user or administrator has to open a file, mount anything, or take any action.\nS:U - The corrupted state is the attacker's own VMA flags and the resulting crash or protection loss stays within the kernel and the process's own address space, without crossing into a hypervisor, IOMMU, or other security authority.\nC:H - Clearing VM_PKEY_BIT0..4 makes vma_pkey() return 0 and drops _PAGE_PKEY_* from the recomputed page protection, silently revoking MPK-based isolation so an untrusted in-process component can read memory it was walled off from; combined with the VM_SEALED drop (allowing mremap of regions the policy pinned) this yields disclosure of memory the kernel was supposed to keep protected.\nI:H - The wipe silently revokes kernel-enforced write protections: VM_SEALED loss is a full mseal(2) bypass (sealed code/GOT regions become mprotect-able and munmap-able), and VM_SHADOW_STACK loss lets userspace write its own CET shadow stack, defeating control-flow integrity and enabling ROP — memory the kernel guaranteed immutable becomes attacker-writable.\nA:H - Dropping VM_UFFD_MINOR while leaving vma->vm_userfaultfd_ctx set creates the inconsistency that userfaultfd_release_all() asserts on, producing a kernel BUG()/invalid-opcode panic on close() (a WARNING at mm/userfaultfd.c:2067 after 31defc3b01d9, still fatal under panic_on_warn). Any local user can trigger this at will."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"include/linux/mm.h",
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"rust/bindings/bindings_helper.h"
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],
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"versions": [
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{
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"version": "63c17fb8e5a46a16e10e82005748837fd11a2024",
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"lessThan": "850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71",
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"status": "affected",
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{
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"product": "Linux",
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"include/linux/mm.h",
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"rust/bindings/bindings_helper.h"
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],
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"versions": [
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"status": "affected"
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"version": "0",
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"versionType": "semver"
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},
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"version": "5.4.302",
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"lessThanOrEqual": "5.4.*",
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"status": "unaffected",
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},
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{
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"lessThanOrEqual": "5.10.*",
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},
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},
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"lessThanOrEqual": "6.6.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.12.55",
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"lessThanOrEqual": "6.12.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.17.3",
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"lessThanOrEqual": "6.17.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.18",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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}
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]
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],
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"cpeApplicability": [
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"nodes": [
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"operator": "OR",
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"negate": false,
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"references": [
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"url": "https://git.kernel.org/stable/c/850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71"
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},
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},
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{
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"url": "https://git.kernel.org/stable/c/b69f19244c2b6475c8a6eb72f0fb0d53509e48cd"
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},
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{
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"url": "https://git.kernel.org/stable/c/41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693"
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},
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{
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"url": "https://git.kernel.org/stable/c/92b82e232b8d8b116ac6e57aeae7a6033db92c60"
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},
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{
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"url": "https://git.kernel.org/stable/c/ac50c6e0a8f91a02b681af81abb2362fbb67cc18"
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},
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{
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"url": "https://git.kernel.org/stable/c/76385629f45740b7888f8fcd83bde955b10f61fe"
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},
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{
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"url": "https://git.kernel.org/stable/c/f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93"
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}
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],
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"title": "mm/ksm: fix flag-dropping behavior in ksm_madvise",
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"x_generator": {
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"engine": "bippy-1.2.0"
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}
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},
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"adp": [
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{
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"metrics": [
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{
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"other": {
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"type": "ssvc",
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"content": {
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"id": "CVE-2025-40040",
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"role": "CISA Coordinator",
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"options": [
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{
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"Exploitation": "none"
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},
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{
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"Automatable": "no"
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},
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{
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"Technical Impact": "total"
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}
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],
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"version": "2.0.3",
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"timestamp": "2026-10-15T21:56:21.086400Z"
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}
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}
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}
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],
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"title": "CISA ADP Vulnrichment",
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"providerMetadata": {
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"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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"shortName": "CISA-ADP",
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"dateUpdated": "2026-10-15T22:02:36.606Z"
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}
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}
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]
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}
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} |