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CVE-2026-80578
fbdev: core: Fix pointer desynchronization in fb_io_read()
Published 2026-08-26 (2 months ago) by the Linux kernel CNA. Subsystem drivers/video. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-80578 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 | fixed | 6.12.105-1 | Update the kernel and reboot. Fixed in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
In fb_io_read(), if copy_to_user() performs a partial copy (e.g., due to a faulty user buffer), the loop adjusts the chunk size 'c' and updates the remaining 'count'. However, the hardware 'src' pointer has already been eagerly advanced by the original chunk size. If the loop is allowed to continue, the read will resume from an incorrect, over-advanced offset. Since the remaining 'count' was only decremented by the successful bytes, this desynchronization causes the next iterations to execute more hardware reads than originally bounded, eventually leading to out-of-bounds I/O reads. Fix this by breaking out of the loop immediately upon a partial copy_to_user(). A partial copy indicates a faulty user buffer, making subsequent read attempts futile. Breaking out ensures we return the number of successfully read bytes without risking out-of-bounds hardware accesses in subsequent mismatched iterations.
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/video/fbdev/core/fb_io_fops.c
- What this is
- FRAMEBUFFER COREMAINTAINERS section matched on drivers/video/fbdev/core/ · Odd Fixes
Check it on the machine
grep -w CONFIG_FB_IOMEM_FOPS /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. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixie, forky, sidYnot built on s390x/s390x
- bookworm · linux-6.12y
- ?
- not established - no Makefile entry for the affected file
- Y
- built in where it is built at all; some flavours do not build it
- y
- built into the kernel image on every flavour - only a patch removes it
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 switch
- CONFIG_FB_IOMEM_FOPS
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
- 2026-08-26 (2 months ago)source
- CVSS
- 7.3 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.12%, higher than 1.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/video
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.5 | 6.6.153 | 42bc07b4e5a3 |
| 6.5 | 6.12.105 | 42a6d8126c19 |
| 6.5 | 6.18.46 | 7ff87a01ae3a |
| 6.5 | 7.1.10 | 7110b7b794a2 |
| 6.5 | 7.2 | 81cc73be40c6 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | 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
- Exploitation requires a local read(2) on /dev/fb* through fb_read() in fb_chrdev.c, which calls fb_io_read() for I/O-mapped framebuffers (efifb, simplefb, embedded/industrial LCD drivers); no network, adjacent-radio, or physical-bus handler reaches this code.
- AC:LAttack complexity, low
- The attacker fully controls read offset, length, and user-buffer layout; mmap/mprotect can force a partial copy_to_user() at a page boundary on the first chunk, desynchronizing src without races, rare configs, or conditions outside attacker control.
- PR:LPrivileges required, low
- Triggering requires only local permission to open /dev/fb* (video group, seat uaccess ACL, or default console user on embedded HMIs, kiosks, and automotive/industrial displays using I/O framebuffers); no CAP_SYS_ADMIN or init-namespace root is needed.
- UI:NUser interaction, none
- Once framebuffer access is available, the attacker triggers the bug solely via crafted read() calls from their own process; no victim, administrator, or other-user interaction is required.
- S:UScope, unchanged
- Impact is confined to the host kernel and MMIO regions behind the framebuffer mapping; it does not cross VM, container, or IOMMU boundaries into a separate security authority.
- C:HConfidentiality impact, high
- Pointer desynchronization lets fb_memcpy_fromio() read past screen_size/smem_len into adjacent MMIO (GPU/display registers, firmware handoff data), copying that hardware memory into the attacker user buffer; out-of-bounds I/O read warrants High confidentiality impact.
- I:LIntegrity impact, low
- Out-of-bounds MMIO reads can hit read-sensitive device registers (clear-on-read, mode or DMA control fields), causing limited but real hardware/display state modification even though no direct arbitrary kernel-memory write primitive is provided.
- A:HAvailability impact, high
- Repeated unbounded I/O reads beyond the mapped framebuffer can hang or reset display/GPU hardware, provoke bus errors or machine checks on some platforms, and fault on unmapped iomem leading to kernel oops or panic.