cbcvebase.
CVE-2025-40040
published 2025-10-28

CVE-2025-40040: In the Linux kernel, the following vulnerability has been resolved: mm/ksm: fix flag-dropping behavior in ksm_madvise syzkaller discovered the following crash…

PriorityP422medium5.5CVSS 3.1
AVLACLPRLUINSUCNINAH
EPSS
0.35%
27.8th percentile
In the Linux kernel, the following vulnerability has been resolved: mm/ksm: fix flag-dropping behavior in ksm_madvise syzkaller discovered the following crash: (kernel BUG) [ 44.607039] ------------[ cut here ]------------ [ 44.607422] kernel BUG at mm/userfaultfd.c:2067! [ 44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI [ 44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none) [ 44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460 [ 44.617726] Call Trace: [ 44.617926] [ 44.619284] userfaultfd_release+0xef/0x1b0 [ 44.620976] __fput+0x3f9/0xb60 [ 44.621240] fput_close_sync+0x110/0x210 [ 44.622222] __x64_sys_close+0x8f/0x120 [ 44.622530] do_syscall_64+0x5b/0x2f0 [ 44.622840] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 44.623244] RIP: 0033:0x7f365bb3f227 Kernel panics because it detects UFFD inconsistency during userfaultfd_release_all(). Specifically, a VMA which has a valid pointer to vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags. The inconsistency is caused in ksm_madvise(): when user calls madvise() with MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode, it accidentally clears all flags stored in the upper 32 bits of vma->vm_flags. Assuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and int are 32-bit wide. This setup causes the following mishap during the &= ~VM_MERGEABLE assignment. VM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000'0000. After ~ is applied, it becomes 0x7fff'ffff unsigned int, which is then promoted to unsigned long before the & operation. This promotion fills upper 32 bits with leading 0s, as we're doing unsigned conversion (and even for a signed conversion, this wouldn't help as the leading bit is 0). & operation thus ends up AND-ing vm_flags with 0x0000'0000'7fff'ffff instead of

Affected

29 ranges· showing 25
VendorProductVersion rangeFixed in
debianlinux< linux 6.1.158-1 (bookworm)linux 6.1.158-1 (bookworm)
debianlinux-6.1< linux 6.1.158-1 (bookworm)linux 6.1.158-1 (bookworm)
linuxlinux
linuxlinux>= 63c17fb8e5a46a16e10e82005748837fd11a2024 < 850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71
linuxlinux>= 63c17fb8e5a46a16e10e82005748837fd11a2024 < 788e5385d0ff69cdba1cabccb9dab8d9647b9239788e5385d0ff69cdba1cabccb9dab8d9647b9239
linuxlinux>= 63c17fb8e5a46a16e10e82005748837fd11a2024 < b69f19244c2b6475c8a6eb72f0fb0d53509e48cdb69f19244c2b6475c8a6eb72f0fb0d53509e48cd
linuxlinux>= 63c17fb8e5a46a16e10e82005748837fd11a2024 < 41cb9fd904fe0c39d52e82dd84dc3c96b7aa969341cb9fd904fe0c39d52e82dd84dc3c96b7aa9693
linuxlinux>= 63c17fb8e5a46a16e10e82005748837fd11a2024 < 92b82e232b8d8b116ac6e57aeae7a6033db92c6092b82e232b8d8b116ac6e57aeae7a6033db92c60
linuxlinux>= 63c17fb8e5a46a16e10e82005748837fd11a2024 < ac50c6e0a8f91a02b681af81abb2362fbb67cc18ac50c6e0a8f91a02b681af81abb2362fbb67cc18
linuxlinux>= 63c17fb8e5a46a16e10e82005748837fd11a2024 < 76385629f45740b7888f8fcd83bde955b10f61fe76385629f45740b7888f8fcd83bde955b10f61fe
linuxlinux>= 63c17fb8e5a46a16e10e82005748837fd11a2024 < f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93
linuxlinux_kernel>= 0 < 6.1.158-16.1.158-1
linuxlinux_kernel>= 0 < 6.12.57-16.12.57-1
linuxlinux_kernel>= 0 < 6.17.6-16.17.6-1
linuxlinux_kernel>= 0 < 5.15.0-173.1835.15.0-173.183
linuxlinux_kernel>= 0 < 6.17.0-14.146.17.0-14.14
linuxlinux_kernel>= 4.6 < 5.4.3025.4.302
linuxlinux_kernel>= 5.11 < 5.15.1975.15.197
linuxlinux_kernel>= 5.16 < 6.1.1586.1.158
linuxlinux_kernel>= 5.5 < 5.10.2475.10.247
linuxlinux_kernel>= 6.13 < 6.17.36.17.3
linuxlinux_kernel>= 6.2 < 6.6.1146.6.114
linuxlinux_kernel>= 6.7 < 6.12.556.12.55
msrcazl3_kernel_6.6.104.2-4_on_azure_linux_3.0
msrcazl3_kernel_6.6.112.1-2_on_azure_linux_3.0

CVSS provenance

nvdv3.15.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
osv7.8HIGH
vendor_ubuntu7.8HIGH
vendor_debian5.5MEDIUM
vendor_msrc5.5MEDIUM
vendor_redhat5.5MEDIUM
Stop checking back — get the weekly exploitation signal.

Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.