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CVE-2026-74675
vt: stabilize tty reference in kbd_keycode with tty_port_tty_get
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem drivers/tty. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74675 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. 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
kbd_keycode() reads vc->port.tty without acquiring a tty reference, racing against con_shutdown() which clears port.tty under a different lock. Use tty_port_tty_get()/tty_kref_put() to hold a proper reference for the duration the tty pointer is needed.
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/tty/vt/keyboard.c
- What this is
- TTY LAYER AND SERIAL DRIVERSMAINTAINERS section matched on drivers/tty/ · linux-kernel@vger.kernel.org · Supported
Check it on the machine
grep -w CONFIG_VT /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, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_VT
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
- 2026-08-22 (2 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
- 0.13%, higher than 2.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/tty
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.12 | 5.10.265 | b84fd400f80a |
| 2.6.12 | 5.15.216 | 38400673c9bf |
| 2.6.12 | 6.1.183 | cab5a342f058 |
| 2.6.12 | 6.6.152 | 38a0aa593ebc |
| 2.6.12 | 6.12.104 | 3f6b1d3fcfc2 |
| 2.6.12 | 6.18.45 | b664592e9ba8 |
| 2.6.12 | 7.1.9 | cc4a1a2ce0c5 |
| 2.6.12 | 7.2 | e25d47a52693 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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 code is reached only through local virtual-console and input paths: kbd_keycode runs from the VT keyboard input handler on key/key-repeat events while con_shutdown runs during final close(2) on /dev/ttyN; there is no network, Bluetooth-only, or remote-protocol reachability to both sides of the race.
- AC:LAttack complexity, low
- The attacker controls both race participants: one thread can loop open/close a console tty to drive release_tty/con_shutdown while another holds a key for repeat events (down==2) or injects EV_KEY via uinput, retrying until kbd_keycode uses a freed tty_struct.
- PR:LPrivileges required, low
- No real-root capability is required; a console-logged-in user with normal DAC access to /dev/ttyN (typical tty-group membership) can close their VT tty and generate foreground key events, and vt_ioctl grants perm to the controlling-tty owner without CAP_SYS_TTY_CONFIG.
- UI:NUser interaction, none
- The attacker performs every step from its own console session—opening/closing the VT tty and generating key or key-repeat input—so no separate victim or administrator action is required.
- S:UScope, unchanged
- The slab use-after-free corrupts kernel heap memory within the same kernel security authority; it does not cross a VM, IOMMU, or sandbox boundary.
- C:HConfidentiality impact, high
- After the tty is freed, kbd_keycode reads freed tty_struct fields (termios for L_ECHO and optionally tty->ops via tty_chars_in_buffer), giving a use-after-free read primitive and enabling disclosure of kernel memory once the slab object is reclaimed.
- I:HIntegrity impact, high
- The path writes tty->driver_data on a freed tty_struct and may indirect-call through tty->ops in tty_chars_in_buffer, enabling heap spray and control-flow hijack for arbitrary kernel modification or privilege escalation.
- A:HAvailability impact, high
- Use-after-free on tty_struct reliably produces kernel oops or panic on illegal dereference through freed memory, and the open/close versus key-repeat race can be retriggered at will for repeatable denial of service.