# CVE-2026-90055: usb: atm: usbatm: fix invalid ci_range initialization

> A local attacker can trigger a shift-out-of-bounds error in the Linux kernel's USB ATM driver, causing a system crash or denial of service.

- **Severity:** Not scored
- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102525, BELL-CVE-2026-90055, DEBIAN-CVE-2026-90055, GHSA-vpcj-fg84-6vgj, UBUNTU-CVE-2026-90055

## What is CVE-2026-90055?

CVE-2026-90055 is a vulnerability in Linux, published on 17 Sep 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:

usb: atm: usbatm: fix invalid ci_range initialization

syzbot reported a shift-out-of-bounds in __vcc_connect():

  UBSAN: shift-out-of-bounds in net/atm/common.c:382:32
  shift exponent -1 is negative
  CPU: 0 UID: 0 PID: 5987 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(full)
  Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
  Call Trace:
   <TASK>
   dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
   ubsan_epilogue+0xa/0x30 lib/ubsan.c:233
   __ubsan_handle_shift_out_of_bounds+0x36d/0x400 lib/ubsan.c:494
   __vcc_connect+0x14b4/0x19c0 net/atm/common.c:382
   vcc_connect+0x328/0x8f0 net/atm/common.c:498
   pvc_bind+0x272/0x380 net/atm/pvc.c:52
   __sys_bind+0x2e3/0x410 net/socket.c:1976
   __x64_sys_bind+0x7a/0x90 net/socket.c:1979
   ...

ATM device ci_range fields (vpi_bits and vci_bits) represent the
number of bits supported for VPI and VCI addressing on the device.
net/atm/common.c directly uses these fields as bit shift counts:
  vpi >> dev->ci_range.vpi_bits
  vci >> dev->ci_range.vci_bits
  1 << vcc->dev->ci_range.vpi_bits
  1 << vcc->dev->ci_range.vci_bits

usbatm_atm_init() sets ci_range.vpi_bits and ci_range.vci_bits to
ATM_CI_MAX (-1), which is defined in <uapi/linux/atmdev.h> as a
sentinel value for userspace ATM_SETCIRANGE requests, not a valid bit
count. Shifting by -1 is undefined behavior and triggers UBSAN
warnings.

ATM UNI cell headers allow up to 8 bits for VPI (0..255) and 16 bits
for VCI (0..65535). Initialize vpi_bits to 8 and vci_bits to 16, as
done by solos-pci.

## Which versions are affected by CVE-2026-90055?


## How do I fix CVE-2026-90055?

Apply the vendor's patch.

## Is CVE-2026-90055 being exploited?

There is no known exploitation of CVE-2026-90055 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90055 and fix it if it is affected.

What it is: CVE-2026-90055 is a vulnerability in Linux, published on 17 Sep 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-2026-90055 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-2026-90055/ (Markdown: https://insights.sbomify.com/CVE-2026-90055/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90055
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90055
- OSV: https://osv.dev/vulnerability/CVE-2026-90055

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90055/
Summaries are generated and may contain mistakes; the official description above is the record.