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CVE-2026-89760
mm, swap: don't free a hibernation slot that is in the swap cache
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-2026-89760 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 | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| 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. |
The vulnerability
What the bug is
A slot with a folio in the swap cache is freed when the folio leaves the cache, not when its count drops. swap_put_entries_cluster() follows that rule. swap_free_hibernation_slot() does not, it calls __swap_cluster_free_entries() whether or not a folio sits on the slot. Cluster readahead can put one there. It walks a raw page_cluster sized window of offsets around the faulting entry, and a hibernation slot passes __swap_cache_add_check() because it is not a folio and its count is not zero. Freeing the slot then clears the entry under that folio. The folio is now unreachable from the swap table, and the offset goes back to the allocator. The folio is still on the LRU though, so reclaim can pick it up later. It then takes the old offset out of folio->swap and overwrites the table entry there, which by then may belong to someone else. This bug can trigger silent memory corruption, process crashes, or data instability across completely unrelated userspace applications - typically occurring when uswsusp is preparing the hibernation image. I found this while working on giving hibernation slots their own marker in the swap table, which I had discussed with Kairui. (https://lore.kernel.org/linux-mm/abp7aDgYLrxF3Me8@KASONG-MC4/) As far as I know there are no reports, so there is no Reported-by/Closes to add. Check for a cached folio before freeing. The slot is then left in the ordinary state where only the swap cache holds it, and it is freed when the folio leaves the cache, either through the reclaim below or through normal reclaim later.
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/swapfile.c
- What this is
- MEMORY MANAGEMENT - SWAPMAINTAINERS section matched on mm/swapfile.c · linux-mm@kvack.org · Maintained
Check it on the machine
grep -w CONFIG_SWAP /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 code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_SWAP
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
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 5.4% 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 |
|---|---|---|
| 7.1 | 7.2.4 | a6df73156f2d |
| 7.1 | 7.3 | 10d9012e83ef |
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 reached only through local hibernation swap alloc/free (/dev/snapshot SNAPSHOT_ALLOC_SWAP_PAGE and SNAPSHOT_FREE_SWAP_PAGES, kernel hibernate()/swsusp_write, or swsusp_unmark) racing with local swapin; it is not reachable from network packets or remote protocols.
- AC:LAttack complexity, low
- The attacker controls cluster readahead via tmpfs/shmem swapin (shmem_swapin_cluster always calls swap_cluster_readahead) in the same percpu cluster that swap_alloc_hibernation_slot uses; SNAPSHOT_ALLOC_SWAP_PAGE does not require a freeze, so neighboring hibernation slots can be cached and the sequence retried at will.
- PR:LPrivileges required, low
- The readahead half needs only an ordinary local account (mmap of /dev/shm, pageout, faults). Hibernation is available to a local seat user via logind/polkit or idle/lid policy on typical laptop, desktop, and embedded systems without init-namespace root.
- UI:NUser interaction, none
- The attacker drives swap activity from their own threads and can start hibernation themselves (logind/systemctl hibernate) or wait for ordinary unattended hibernation; no separate victim action such as mounting a filesystem or opening a file is required.
- S:UScope, unchanged
- Corruption stays in the host kernel swap table and the same kernel's anonymous/shmem pages; this is standard local kernel impact, not a VM escape, IOMMU/DMA bypass, or other cross-authority boundary.
- C:HConfidentiality impact, high
- Freeing a swap-cache folio's hibernation slot returns that offset to the allocator while the folio remains on the LRU; later reclaim overwrites a reused swap-table entry so another task can be given the stale folio, disclosing hibernation-image or other processes' memory.
- I:HIntegrity impact, high
- The same stale-folio reclaim writes into a swap-table slot that may already hold another folio pointer or swap count, corrupting MM metadata and yielding a kernel write/type-confusion primitive suitable for control-flow hijack rather than a bounded integrity change.
- A:HAvailability impact, high
- The commit documents silent memory corruption and process crashes across unrelated userspace; a reused swap-table entry overwritten with a stale or non-folio value oopses or panics on swapin and can repeatedly crash the system.