# 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.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 22 Aug 2026
- **Updated:** 27 Aug 2026
- **Also known as:** BELL-CVE-2026-74655, DEBIAN-CVE-2026-74655, GHSA-fpvh-p63v-qp88, UBUNTU-CVE-2026-74655

## 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.

## Is CVE-2026-74655 being exploited?

There is no known exploitation of CVE-2026-74655 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74655 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-74655 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74655/ (Markdown: https://insights.sbomify.com/CVE-2026-74655/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74655
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74655
- OSV: https://osv.dev/vulnerability/CVE-2026-74655

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74655/
Summaries are generated and may contain mistakes; the official description above is the record.