# CVE-2025-39993: media: rc: fix races with imon_disconnect()

> A race condition in the Linux kernel iMON driver allows a use-after-free, potentially enabling local attackers to execute code or escalate privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/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:** 15 Oct 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-39993, DEBIAN-CVE-2025-39993, GHSA-2c3m-5h4x-9w2g, ROOT-OS-DEBIAN-11-CVE-2025-39993, ROOT-OS-DEBIAN-12-CVE-2025-39993, ROOT-OS-DEBIAN-13-CVE-2025-39993, ROOT-OS-UBUNTU-2204-CVE-2025-39993, ROOT-OS-UBUNTU-2404-CVE-2025-39993, UBUNTU-CVE-2025-39993

## What is CVE-2025-39993?

CVE-2025-39993 is a high-severity use after free vulnerability in Linux, published on 15 Oct 2025. 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:

media: rc: fix races with imon_disconnect()

Syzbot reports a KASAN issue as below:
BUG: KASAN: use-after-free in __create_pipe include/linux/usb.h:1945 [inline]
BUG: KASAN: use-after-free in send_packet+0xa2d/0xbc0 drivers/media/rc/imon.c:627
Read of size 4 at addr ffff8880256fb000 by task syz-executor314/4465

CPU: 2 PID: 4465 Comm: syz-executor314 Not tainted 6.0.0-rc1-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
Call Trace:
 <TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:317 [inline]
print_report.cold+0x2ba/0x6e9 mm/kasan/report.c:433
kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
__create_pipe include/linux/usb.h:1945 [inline]
send_packet+0xa2d/0xbc0 drivers/media/rc/imon.c:627
vfd_write+0x2d9/0x550 drivers/media/rc/imon.c:991
vfs_write+0x2d7/0xdd0 fs/read_write.c:576
ksys_write+0x127/0x250 fs/read_write.c:631
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

The iMON driver improperly releases the usb_device reference in
imon_disconnect without coordinating with active users of the
device.

Specifically, the fields usbdev_intf0 and usbdev_intf1 are not
protected by the users counter (ictx->users). During probe,
imon_init_intf0 or imon_init_intf1 increments the usb_device
reference count depending on the interface. However, during
disconnect, usb_put_dev is called unconditionally, regardless of
actual usage.

As a result, if vfd_write or other operations are still in
progress after disconnect, this can lead to a use-after-free of
the usb_device pointer.

Thread 1 vfd_write                      Thread 2 imon_disconnect
                                        ...
                                        if
                                          usb_put_dev(ictx->usbdev_intf0)
                                        else
                                          usb_put_dev(ictx->usbdev_intf1)
...
while
  send_packet
    if
      pipe = usb_sndintpipe(
        ictx->usbdev_intf0) UAF
    else
      pipe = usb_sndctrlpipe(
        ictx->usbdev_intf0, 0) UAF

Guard access to usbdev_intf0 and usbdev_intf1 after disconnect by
checking ictx->disconnected in all writer paths. Add early return
with -ENODEV in send_packet(), vfd_write(), lcd_write() and
display_open() if the device is no longer present.

Set and read ictx->disconnected under ictx->lock to ensure memory
synchronization. Acquire the lock in imon_disconnect() before setting
the flag to synchronize with any ongoing operations.

Ensure writers exit early and safely after disconnect before the USB
core proceeds with cleanup.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

## Which versions are affected by CVE-2025-39993?


## How do I fix CVE-2025-39993?

Apply the vendor's patch.

## Is CVE-2025-39993 being exploited?

There is no known exploitation of CVE-2025-39993 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-39993 and fix it if it is affected.

What it is: CVE-2025-39993 is a high-severity use after free vulnerability in Linux, published on 15 Oct 2025. 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-2025-39993 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-2025-39993/ (Markdown: https://insights.sbomify.com/CVE-2025-39993/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39993
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39993
- OSV: https://osv.dev/vulnerability/CVE-2025-39993

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39993/
Summaries are generated and may contain mistakes; the official description above is the record.