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CVE-2026-64449
staging: vme_user: bound slave read/write to the kern_buf size
Published 2026-07-25 (3 months ago) by the Linux kernel CNA. Subsystem drivers/staging. Debian urgency: not yet assigned.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-64449 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 | fixedDLA-4720-1 · 2026-08-05 · text | 6.1.180-1 | Update the kernel and reboot. DLA-4720-1 shipped the fix on 2026-08-05, in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.96-1 | Update the kernel and reboot. Fixed in 6.12.96-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The SLAVE-path helpers buffer_to_user() and buffer_from_user() copy 'count' bytes into/out of the fixed-size kern_buf (size_buf == PCI_BUF_SIZE == 0x20000, 128 KiB) using *ppos as the offset, without bounding *ppos + count against size_buf. vme_user_write()/vme_user_read() only clamp count to the VME window size (image_size = vme_get_size(resource)), which VME_SET_SLAVE sets from the user-supplied slave.size -- validated against the VME address space (up to VME_A32_MAX = 4 GiB), not against PCI_BUF_SIZE. When the window exceeds 128 KiB, a write()/read() copies past the kern_buf allocation. Clamp count against size_buf in both helpers, with an early return when *ppos is already at/after the buffer end. *ppos is >= 0 here (the caller rejects negative offsets), so size_buf - *ppos cannot wrap. This mirrors the existing clamp in the MASTER-path helpers resource_to_user() / resource_from_user(), and matches the read()/write() convention of a short transfer at end-of-buffer. Found by static analysis (CodeQL taint tracking + CBMC bounded model checking) and confirmed dynamically under KASAN with the vme_fake bridge: BUG: KASAN: slab-out-of-bounds in _copy_from_user+0x2d/0x80 Write of size 262144 at addr ffff888004100000 by task trigger/68 _copy_from_user+0x2d/0x80 vme_user_write+0x13e/0x240 [vme_user] vfs_write+0x1b8/0x7a0 ksys_write+0xb8/0x150
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/staging/vme_user/vme_user.c
- What this is
- VME SUBSYSTEMMAINTAINERS section matched on drivers/staging/vme_user/ · linux-kernel@vger.kernel.org · Orphan
- Kernel module
- none to look for. The file would have gone into vme_user, and Debian does not compile it into that module, so finding vme_user in lsmod would say nothing about this CVE.
Check it on the machine
grep -wE 'CONFIG_STAGING|CONFIG_VME_BUS|CONFIG_VME_USER' /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 5 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12n
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_STAGING, CONFIG_VME_BUS, CONFIG_VME_USER
- 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
- 2026-07-25 (3 months 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
- 0.14%, higher than 2.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/staging
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.32 | 6.1.178 | 65358d89dc9f |
| 2.6.32 | 6.6.145 | adc8b9c30d71 |
| 2.6.32 | 6.12.96 | 8eff7cd4817e |
| 2.6.32 | 6.18.39 | e99f2df433c6 |
| 2.6.32 | 7.1.4 | 1b495fa0d492 |
| 2.6.32 | 7.2 | 9f32f3826501 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DLA-4723-1 | 2026-08-07 | bullseye 6.1.180-1~deb11u1 | tracker |
| DLA-4720-1 | 2026-08-05 | bookworm 6.1.180-1 | 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 vulnerable path is reached through ioctl(), lseek(), read(), and write() on a local /dev/bus/vme/s* character device. Network or physical VME-bus input is not needed.
- AC:LAttack complexity, low
- The attacker can deterministically configure an aligned slave window larger than 128 KiB and select the copy offset and length; no race or external condition is required. A 256 KiB overflow was dynamically confirmed under KASAN.
- PR:LPrivileges required, low
- The driver performs no capability or namespace-specific check, so an ordinary account granted access to the VME device node can configure and trigger the flaw. Although devtmpfs defaults to root-owned mode 0600, non-root access for an industrial control or service account is a reasonable deployment.
- UI:NUser interaction, none
- The attacker independently performs the configuration and malicious read or write without requiring any victim action.
- S:UScope, unchanged
- Exploitation compromises the host kernel within the same security authority. This is a standard local privilege-escalation condition, not a VM, sandbox, or IOMMU boundary escape.
- C:HConfidentiality impact, high
- The read path copies an attacker-selected, potentially very large range of kernel memory beyond the 128 KiB allocation to userspace. This can disclose adjacent allocations, kernel pointers, credentials, and other sensitive memory.
- I:HIntegrity impact, high
- The write path copies attacker-controlled bytes beyond the DMA or large-kmalloc allocation, potentially across many adjacent physical pages. This provides exploitable memory corruption capable of modifying kernel objects or achieving control-flow hijacking.
- A:HAvailability impact, high
- The out-of-bounds write was confirmed to trigger a KASAN kernel memory-safety failure and can corrupt or access invalid adjacent memory. A kernel oops or panic can be triggered without user interaction.