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CVE-2026-80958
dm-pcache: clamp the tail kset read to the segment data region
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem drivers/md. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-80958 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 tail-kset read in cache_replay(), the writeback worker and the GC worker bounds its length by PCACHE_SEG_SIZE - seg_off, the raw segment size rather than the data region. A tail near the segment end reads past the segment data into the following control area. Clamp the read to cache_seg_remain(), the data region.
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/md/dm-pcache/cache_gc.c
drivers/md/dm-pcache/cache_key.c
drivers/md/dm-pcache/cache_writeback.c
- What this is
- DEVICE-MAPPER PCACHE TARGETMAINTAINERS section matched on drivers/md/dm-pcache/ · dm-devel@lists.linux.dev · Maintained
Check it on the machine
grep -wE 'CONFIG_DM_PCACHE|CONFIG_MD' /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 does not build this code in 2 releases. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidn
- ?
- not established - no Makefile entry for the affected file
- n
- not enabled on any flavour - this release does not build the code
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_DM_PCACHE, CONFIG_MD
- Reads as
- all on means the file is compiled; any one off means it is not.
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:H/I:N/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 5.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/md
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.18 | 6.18.50 | 2cd9776fe3f2 |
| 6.18 | 7.2.4 | 1ab55354368d |
| 6.18 | 7.3 | becf07e2b005 |
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 over-read is reached only through local device-mapper ioctls on /dev/mapper/control (ctl_ioctl requires CAP_SYS_ADMIN, then table_load → dm_pcache_ctr → pcache_cache_start → cache_replay), and later via the writeback and GC workers on that mapped device; no network, Bluetooth, or physical-bus input reaches the kset copy.
- AC:LAttack complexity, low
- An attacker who supplies a crafted DAX/pmem cache image fully controls the persisted key_tail and dirty_tail, so placing a tail near the segment end deterministically copies past data_size; no race, heap layout, or other victim state outside attacker control is required.
- PR:LPrivileges required, low
- dm-ioctl.c gates table load with capable(CAP_SYS_ADMIN), which user-namespace and privileged-container administrators satisfy without init-namespace root; the attacker can attach a DAX cache device they control and load the pcache table themselves.
- UI:NUser interaction, none
- Exploitation requires only the attacker's own dmsetup/DM_TABLE_LOAD of a crafted pcache cache device; no separate victim must mount media, open files, or take any other action.
- S:UScope, unchanged
- The out-of-bounds kset read and any resulting kernel oops remain inside the host kernel device-mapper/pcache subsystem; this is not a VM escape, IOMMU bypass, or other cross-authority breakout.
- C:HConfidentiality impact, high
- copy_mc_to_kernel() copies up to PCACHE_KSET_ONMEDIA_SIZE_MAX (~5 KiB) past segment data_size into the next segment's control area, and on the last segment that continues beyond the DAX mapping into adjacent kernel memory; out-of-bounds reads are High unless limited to a few bytes.
- I:NIntegrity impact, none
- The destination is a correctly sized kset buffer (kzalloc or the writeback/GC scratch arrays); this is a source over-read, not an out-of-bounds write, use-after-free, or other kernel-memory corruption or control-flow hijack primitive.
- A:HAvailability impact, high
- Reading past the last DAX-mapped page hits a vmap guard or unmapped hole and oopses the kernel, and a CRC-valid kset assembled across the data/control boundary that is larger than cache_seg_remain() hits BUG_ON in cache_pos_advance(), crashing the host.