# CVE-2025-40048: uio_hv_generic: Let userspace take care of interrupt mask

> A race condition in the uio_hv_generic driver can cause user-space processes to hang indefinitely by missing interrupts.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Oct 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-68909, BELL-CVE-2025-40048, DEBIAN-CVE-2025-40048, GHSA-hw92-4498-rgw4, ROOT-OS-DEBIAN-11-CVE-2025-40048, ROOT-OS-DEBIAN-12-CVE-2025-40048, ROOT-OS-DEBIAN-13-CVE-2025-40048, ROOT-OS-UBUNTU-2204-CVE-2025-40048, ROOT-OS-UBUNTU-2404-CVE-2025-40048, UBUNTU-CVE-2025-40048

## What is CVE-2025-40048?

CVE-2025-40048 is a high-severity vulnerability in Linux, published on 28 Oct 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

uio_hv_generic: Let userspace take care of interrupt mask

Remove the logic to set interrupt mask by default in uio_hv_generic
driver as the interrupt mask value is supposed to be controlled
completely by the user space. If the mask bit gets changed
by the driver, concurrently with user mode operating on the ring,
the mask bit may be set when it is supposed to be clear, and the
user-mode driver will miss an interrupt which will cause a hang.

For eg- when the driver sets inbound ring buffer interrupt mask to 1,
the host does not interrupt the guest on the UIO VMBus channel.
However, setting the mask does not prevent the host from putting a
message in the inbound ring buffer. So let’s assume that happens,
the host puts a message into the ring buffer but does not interrupt.

Subsequently, the user space code in the guest sets the inbound ring
buffer interrupt mask to 0, saying “Hey, I’m ready for interrupts”.
User space code then calls pread() to wait for an interrupt.
Then one of two things happens:

* The host never sends another message. So the pread() waits forever.
* The host does send another message. But because there’s already a
  message in the ring buffer, it doesn’t generate an interrupt.
  This is the correct behavior, because the host should only send an
  interrupt when the inbound ring buffer transitions from empty to
  not-empty. Adding an additional message to a ring buffer that is not
  empty is not supposed to generate an interrupt on the guest.
  Since the guest is waiting in pread() and not removing messages from
  the ring buffer, the pread() waits forever.

This could be easily reproduced in hv_fcopy_uio_daemon if we delay
setting interrupt mask to 0.

Similarly if hv_uio_channel_cb() sets the interrupt_mask to 1,
there’s a race condition. Once user space empties the inbound ring
buffer, but before user space sets interrupt_mask to 0, the host could
put another message in the ring buffer but it wouldn’t interrupt.
Then the next pread() would hang.

Fix these by removing all instances where interrupt_mask is changed,
while keeping the one in set_event() unchanged to enable userspace
control the interrupt mask by writing 0/1 to /dev/uioX.

## Which versions are affected by CVE-2025-40048?


## How do I fix CVE-2025-40048?

Apply the vendor's patch.

## Is CVE-2025-40048 being exploited?

There is no known exploitation of CVE-2025-40048 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40048 and fix it if it is affected.

What it is: CVE-2025-40048 is a high-severity vulnerability in Linux, published on 28 Oct 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40048 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-2025-40048/ (Markdown: https://insights.sbomify.com/CVE-2025-40048/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40048
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40048
- OSV: https://osv.dev/vulnerability/CVE-2025-40048

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40048/
Summaries are generated and may contain mistakes; the official description above is the record.