# CVE-2024-26996: usb: gadget: f_ncm: Fix UAF ncm object at re-bind after usb ep transport error

> A use-after-free vulnerability in the Linux kernel's NCM USB gadget driver allows attackers to cause a system crash or potentially execute code via crafted USB interactions.

- **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:** 1 May 2024
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2024-26996, DEBIAN-CVE-2024-26996, GHSA-2wc3-h48p-9gpq, ROOT-OS-DEBIAN-11-CVE-2024-26996, UBUNTU-CVE-2024-26996

## What is CVE-2024-26996?

CVE-2024-26996 is a high-severity use after free vulnerability in Linux kernel, published on 1 May 2024. 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:

usb: gadget: f_ncm: Fix UAF ncm object at re-bind after usb ep transport error

When ncm function is working and then stop usb0 interface for link down,
eth_stop() is called. At this piont, accidentally if usb transport error
should happen in usb_ep_enable(), 'in_ep' and/or 'out_ep' may not be enabled.

After that, ncm_disable() is called to disable for ncm unbind
but gether_disconnect() is never called since 'in_ep' is not enabled.

As the result, ncm object is released in ncm unbind
but 'dev->port_usb' associated to 'ncm->port' is not NULL.

And when ncm bind again to recover netdev, ncm object is reallocated
but usb0 interface is already associated to previous released ncm object.

Therefore, once usb0 interface is up and eth_start_xmit() is called,
released ncm object is dereferrenced and it might cause use-after-free memory.

[function unlink via configfs]
  usb0: eth_stop dev->port_usb=ffffff9b179c3200
  --> error happens in usb_ep_enable().
  NCM: ncm_disable: ncm=ffffff9b179c3200
  --> no gether_disconnect() since ncm->port.in_ep->enabled is false.
  NCM: ncm_unbind: ncm unbind ncm=ffffff9b179c3200
  NCM: ncm_free: ncm free ncm=ffffff9b179c3200   <-- released ncm

[function link via configfs]
  NCM: ncm_alloc: ncm alloc ncm=ffffff9ac4f8a000
  NCM: ncm_bind: ncm bind ncm=ffffff9ac4f8a000
  NCM: ncm_set_alt: ncm=ffffff9ac4f8a000 alt=0
  usb0: eth_open dev->port_usb=ffffff9b179c3200  <-- previous released ncm
  usb0: eth_start dev->port_usb=ffffff9b179c3200 <--
  eth_start_xmit()
  --> dev->wrap()
  Unable to handle kernel paging request at virtual address dead00000000014f

This patch addresses the issue by checking if 'ncm->netdev' is not NULL at
ncm_disable() to call gether_disconnect() to deassociate 'dev->port_usb'.
It's more reasonable to check 'ncm->netdev' to call gether_connect/disconnect
rather than check 'ncm->port.in_ep->enabled' since it might not be enabled
but the gether connection might be established.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2024-26996?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-26996?

Apply the vendor's patch.

## Is CVE-2024-26996 being exploited?

There is no known exploitation of CVE-2024-26996 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-26996 and fix it if it is affected.

What it is: CVE-2024-26996 is a high-severity use after free vulnerability in Linux kernel, published on 1 May 2024. 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-2024-26996 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2024-26996/ (Markdown: https://insights.sbomify.com/CVE-2024-26996/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-26996
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-26996
- OSV: https://osv.dev/vulnerability/CVE-2024-26996

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-26996/
Summaries are generated and may contain mistakes; the official description above is the record.