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CVE-2026-90043
zram: fix slot lock bit position on big-endian 64-bit
Published 2026-09-16 (33 days ago) by the Linux kernel CNA. Subsystem drivers/block. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-90043 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
The slot lock is a bit operation on the whole __lock word, which flags and ac_time alias as two u32s. On little-endian the lock bit lands in the position ZRAM_ENTRY_LOCK reserves in flags, so the aliasing works out. On 64-bit big-endian it lands in ac_time instead: with ZRAM_TRACK_ENTRY_ACTIME enabled, storing the access time from mark_slot_accessed() or slot_free() wipes out the held lock bit, letting another CPU take the same slot lock; an access time value with that bit set makes the slot look locked forever. Shift the lock bit into the flags half of the word on big-endian 64-bit.
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.
drivers/block/zram/zram_drv.c
drivers/block/zram/zram_drv.h
- What this is
- ZRAM COMPRESSED RAM BLOCK DEVICE DRVIERMAINTAINERS section matched on drivers/block/zram/ · linux-kernel@vger.kernel.org · Maintained
- Kernel module
- zram
Check it on the machine
grep -w CONFIG_ZRAM /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.
lsmod | grep -w zramPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_ZRAM
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
- 2026-09-16 (33 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
- drivers/block
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 7.0 | 7.2.5 | 052b6b2d5fe9 |
| 7.0 | 7.3 | a8b5875741d4 |
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 broken slot lock lives in the zram block driver and is reached only through local I/O: zram_submit_bio() for read/write/discard and zram_slot_free_notify() from swap. It is not in a network protocol parser, Bluetooth/WiFi path, or a physical-device driver.
- AC:LAttack complexity, low
- On 64-bit big-endian kernels with CONFIG_ZRAM_TRACK_ENTRY_ACTIME, slot_free() zeros ac_time (the lock bit) immediately after slot_lock(), so exclusion is dropped on every free. An attacker who issues concurrent reads, writes, discards, or swap faults against the same zram page controls both sides of the race.
- PR:LPrivileges required, low
- zram_open() and zram_submit_bio() impose no capability check. In the highest-impact setup zram is already swap or mounted scratch storage, so an unprivileged local user can induce paging or file I/O that hits the slot lock; admin-only device creation is only an environmental prerequisite.
- UI:NUser interaction, none
- After zram is configured as swap or writable storage, the attacker triggers the vulnerable path directly via memory pressure, page faults, madvise, or ordinary file I/O. No victim must mount a filesystem, open a crafted file, or otherwise participate.
- S:UScope, unchanged
- Impact is corruption of in-kernel zram table entries and zsmalloc objects on the same host. That is a standard kernel compromise and does not cross a VM, IOMMU, or other separate security authority.
- C:HConfidentiality impact, high
- Clearing the held slot lock lets one CPU zs_free() a zsmalloc object while another still maps it in read_from_zspool()/zs_obj_read_begin(). That use-after-free of compressed-page heap objects can be reused for arbitrary kernel reads.
- I:HIntegrity impact, high
- The same lost exclusion allows double-free of zsmalloc handles and torn updates of slot handle and flags, so a racing writer can free an object another CPU still uses or install a new handle over a live one, enabling arbitrary kernel writes and control-flow hijack.
- A:HAvailability impact, high
- Concurrent zs_free versus zs_obj_read_begin on the same handle can oops or panic the kernel, and an ac_time value that leaves the lock bit set makes later wait_on_bit_lock() sleep uninterruptibly forever on that slot.