# CVE-2026-74276: spi: xilinx: use FIFO occupancy register to determine buffer size

> A logic error in the Xilinx SPI driver causes an infinite loop when reading RX FIFO, leading to a denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-74276, DEBIAN-CVE-2026-74276, GHSA-h2g9-c4gr-qg58, UBUNTU-CVE-2026-74276

## What is CVE-2026-74276?

CVE-2026-74276 is a denial of service vulnerability in Linux, published on 15 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:

spi: xilinx: use FIFO occupancy register to determine buffer size

The method the driver uses to determine the size of the FIFO has a
problem. What it currently does is this:
It stops the SPI hardware and writes to the TX FIFO register until TX
FIFO FULL asserts in the status register. But the hardware does not only
have the FIFO, it also has a shift register which can hold a byte. This
can be seen, when writing a byte to the FIFO (while the SPI hardware is
stopped,) the TX FIFO EMPTY is still empty. So, if we have a FIFO size
of 16 for example, the current method returns a 17.
This is a problem, at least when using the driver in irq mode. The same
size determined for the TX FIFO is also assumed for the RX FIFO. When a
SPI transaction wants to write the amount of the FIFO size or more
bytes, the following happens, for example with 16 bytes FIFO size:
The driver stops the SPI hardware and writes 17 bytes to the TX FIFO and
starts the SPI hardware and goes sleep.
The hardware then shifts out 17 bytes (FIFO + shift register) and
simultaneously reads bytes into the RX FIFO, but it only has 16 places,
so it looses one byte. Then TX FIFO empty asserts, wakes the driver
again, which has a fast path and reads 16 bytes from the RX FIFO, but
before reading the last 17th byte (which is lost) it does this:

	sr = xspi->read_fn(xspi->regs + XSPI_SR_OFFSET);
	if (!(sr & XSPI_SR_RX_EMPTY_MASK)) {
		xilinx_spi_rx(xspi);
		rx_words--;
	}

It reads the status register and checks if the RX FIFO is not empty.
But it is empty in our case. So this check spins in a while loop
forever locking the driver.

This patch fixes the logic to determine the FIFO size.

## Which versions are affected by CVE-2026-74276?


## How do I fix CVE-2026-74276?

Apply the vendor's patch.

## Is CVE-2026-74276 being exploited?

There is no known exploitation of CVE-2026-74276 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74276 and fix it if it is affected.

What it is: CVE-2026-74276 is a denial of service vulnerability in Linux, published on 15 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-2026-74276 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-2026-74276/ (Markdown: https://insights.sbomify.com/CVE-2026-74276/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74276
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74276
- OSV: https://osv.dev/vulnerability/CVE-2026-74276

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74276/
Summaries are generated and may contain mistakes; the official description above is the record.