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CVE-2026-89593
hugetlb: only adjust reservation during unmapping if mapcount is 0
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem mm. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-89593 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Since df7a6d1f6405, __unmap_hugepage_range can adjust reservations. In the case of folio mapped in both a parent and a child, if the parent unmaps the range first, the reservation adjustment will result in an underflow of the reserved count. Once the child unmaps the range, the count is restored. Change __unmap_hugepage_range() to check the mapcount before adjusting the reservation.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
mm/hugetlb.c
- What this is
- HUGETLB SUBSYSTEMMAINTAINERS section matched on mm/hugetlb.c · linux-mm@kvack.org · Maintained
Check it on the machine
grep -w CONFIG_HUGETLBFS /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormYnot built on armhf/armmp, armhf/rt/armmp
- trixieYnot built on armel/rpi, armhf/armmp, armhf/rt/armmp
- forky, sidYnot built on armhf/armmp
- bookworm · linux-6.12Ynot built on armhf/armmp, armhf/rt/armmp
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_HUGETLBFS
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.12%, higher than 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- mm
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.9 | 6.12.110 | b0b1b9ca80b7 |
| 6.9 | 6.18.50 | a3c65af20cce |
| 6.9 | 7.2.4 | 0f001491e5a2 |
| 6.9 | 7.3 | 5120b1e048d4 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bug is in __unmap_hugepage_range() on munmap/madvise of a private MAP_HUGETLB VMA after fork, reached only via local mmap/fault/fork/unmap syscalls, not from any network protocol or remote packet path.
- AC:LAttack complexity, low
- Triggering is a deterministic sequence: MAP_PRIVATE|MAP_ANONYMOUS|MAP_HUGETLB mmap, fault the page, fork, then munmap in the parent while the child keeps the mapping. The reporter's reproducer underflows HugePages_Rsvd on every run with no race.
- PR:LPrivileges required, low
- mmap(MAP_ANONYMOUS|MAP_HUGETLB) uses hugetlb_file_setup(HUGETLB_ANONHUGE_INODE) with no CAP_IPC_LOCK check. An unprivileged local user on a host with hugepages (typical for VMs, databases, DPDK, and HPC) can exercise this path, including from a user namespace.
- UI:NUser interaction, none
- The attacker creates the private hugetlb mapping, forks, and unmaps in their own processes; no action by another user or administrator is required.
- S:UScope, unchanged
- Impact is corruption of the host kernel's global hugetlb reservation counter (h->resv_huge_pages) within the same kernel security domain; it does not escape a VM, bypass an IOMMU, or cross another authority.
- C:NConfidentiality impact, none
- The flaw only underflows and wraps the hugepage reservation counter; it does not provide an out-of-bounds read, use-after-free, or other primitive that discloses kernel memory or confidential data.
- I:HIntegrity impact, high
- Parent unmap while a child still maps the folio restores the reserve map, then hugetlb_vm_op_close() decrements resv_huge_pages from zero and wraps it to ULONG_MAX, corrupting global reservation accounting so later allocations can steal hugepages reserved for other tenants and bypass reservation guarantees.
- A:HAvailability impact, high
- With resv_huge_pages wrapped, available_huge_pages() and gather_surplus_pages() treat the pool as having extra pages, so other hugepage users (QEMU, databases, DPDK) can be denied reserved pages and SIGBUS. The attacker controls the child lifetime, so broken accounting can persist and remain desynchronized.