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CVE-2026-74652
serial: amba-pl011: cancel RS485 hrtimers after freeing IRQ
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem drivers/tty. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74652 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 | 7.1.9-1 | 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. |
The vulnerability
What the bug is
The RS485 trigger hrtimers are embedded in the devm-managed port and can fire after it is freed. The IRQ handler can arm a timer, so free the IRQ first and then cancel both timers. Complete the RS485 stop without arming a timer, and cancel the timers in remove() for the suspend-then-unbind path, where shutdown is not called. This issue was found by an in-house static analysis tool.
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/serial/amba-pl011.c
- What this is
- ARM PRIMECELL UART PL010 AND PL011 DRIVERSMAINTAINERS section matched on drivers/tty/serial/amba-pl01*.c · Odd Fixes
Check it on the machine
grep -w CONFIG_SERIAL_AMBA_PL011 /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.
- bookwormYnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, i386/686, i386/686-pae, i386/rt/686-pae, ppc64el/powerpc64le
- trixieYnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidYnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt-amd64, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_SERIAL_AMBA_PL011
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
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.14 | 6.18.45 | 759ead98a39f |
| 6.14 | 7.1.9 | e57f0aa5c35b |
| 6.14 | 7.2 | 36672c8d7d14 |
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 bug is in the PL011 UART/RS485 driver and is reached only via local tty access (open/ioctl TIOCSRS485, write, close) on /dev/ttyAMA* or similar nodes; it is not reachable from the network or from RS485 bus traffic alone without local device control.
- AC:LAttack complexity, low
- An attacker with tty access can enable RS485, queue TX with RTS delay timers, and close or race teardown to arm hrtimers during shutdown/remove; they control both the TX state machine and teardown timing, making the race reliably triggerable.
- PR:LPrivileges required, low
- Exploitation requires write access to the UART tty device (typically dialout group membership), not root; ioctl/write/close drive the RS485 timers and buggy shutdown path, while the suspend-then-unbind heap UAF needs admin but is not the minimum privilege bar.
- UI:NUser interaction, none
- No victim interaction is required; the attacker who holds the tty fd performs TIOCSRS485, transmission, and port close or coordinates teardown themselves without needing another user to act.
- S:UScope, unchanged
- Impact is confined to kernel memory and hardware on the same host (crash, corruption, potential privilege escalation); it does not cross VM, container, or IOMMU security boundaries.
- C:HConfidentiality impact, high
- RS485 hrtimers embedded in the devm uart_amba_port can fire after the port is freed during remove or buggy shutdown, causing a use-after-free that exposes freed kernel heap contents and enables arbitrary memory read primitives.
- I:HIntegrity impact, high
- UAF timer callbacks (pl011_trigger_start_tx/pl011_trigger_stop_tx) continue operating on freed uart_amba_port memory, performing MMIO reads/writes and state updates that enable heap grooming and kernel data corruption or control-flow hijacking.
- A:HAvailability impact, high
- Use-after-free and concurrent hrtimer callbacks during/after port teardown can cause kernel oops, panic, or hang; RS485 timers may also fire on a partially shut down UART, destabilizing the system.