CVE-2026-74655 serial: qcom-geni: fix TX DMA buffer flush
A local attacker can cause a permanent hang in the Qualcomm GENI UART driver by triggering a race condition during transmit flushing, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74655?
CVE-2026-74655 is a high-severity denial of service vulnerability in Linux, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
serial: qcom-geni: fix TX DMA buffer flush
When transmit flushing a qcom-geni UART during an ongoing TX DMA, the UART gets stuck infinitely repeating corrupted TX DMA frames.
The DMA-mode uart_ops does not provide a flush_buffer callback, so an in-flight transfer can complete after serial core has reset the transmit kfifo, underflowing its length and resubmitting page-sized transfers indefinitely. Add one that stops the transfer and clears tx_remaining and tx_queued.
The stop path was also broken: it unmapped the buffer while the serial engine could still read it, and never reset the TX DMA state machine. Cancel the main sequencer command first, then reset the state machine and wait for it before unmapping. Drop the early return so a pending mapping is also cleaned up when the main command is inactive.
The bug can be triggered from userspace with a large write immediately followed by TCOFLUSH. A following tcdrain will hang forever. The bug was reproduced and this fix was validated on Arduino Uno Q (QRB2210) using /dev/ttyHS1.
Which versions are affected by CVE-2026-74655?
How do I fix CVE-2026-74655?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-74655 being exploited?
There is no known exploitation of CVE-2026-74655 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-74655, DEBIAN-CVE-2026-74655, GHSA-fpvh-p63v-qp88, UBUNTU-CVE-2026-74655.