# CVE-2026-53306: tty: hvc_iucv: fix off-by-one in number of supported devices

> An off-by-one error in the Linux kernel's hvc_iucv driver allows out-of-bounds memory access, potentially leading to system instability or crashes.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 26 Jun 2026
- **Updated:** 26 Jun 2026
- **Also known as:** BELL-CVE-2026-53306, DEBIAN-CVE-2026-53306, GHSA-v222-hvcr-rghc, ROOT-OS-DEBIAN-11-CVE-2026-53306, ROOT-OS-DEBIAN-12-CVE-2026-53306, ROOT-OS-UBUNTU-2204-CVE-2026-53306, ROOT-OS-UBUNTU-2404-CVE-2026-53306, UBUNTU-CVE-2026-53306

## What is CVE-2026-53306?

CVE-2026-53306 is a medium-severity vulnerability in Linux kernel, published on 26 Jun 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:

tty: hvc_iucv: fix off-by-one in number of supported devices

MAX_HVC_IUCV_LINES == HVC_ALLOC_TTY_ADAPTERS == 8.
This is the number of entries in:
  static struct hvc_iucv_private *hvc_iucv_table[MAX_HVC_IUCV_LINES];

Sometimes hvc_iucv_table[] is limited by:
(a)	if (num > hvc_iucv_devices) // for error detection
or
(b)	for (i = 0; i < hvc_iucv_devices; i++) // in 2 places
(so these 2 don't agree; second one appears to be correct to me.)

hvc_iucv_devices can be 0..8. This is a counter.
(c)	if (hvc_iucv_devices > MAX_HVC_IUCV_LINES)

If hvc_iucv_devices == 8, (a) allows the code to access hvc_iucv_table[8].
Oops.

Weakness: CWE-193 (Off-by-one Error)

## Which versions are affected by CVE-2026-53306?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53306?

Apply the vendor's patch.

## Is CVE-2026-53306 being exploited?

There is no known exploitation of CVE-2026-53306 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-2026-53306 and fix it if it is affected.

What it is: CVE-2026-53306 is a medium-severity vulnerability in Linux kernel, published on 26 Jun 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-2026-53306 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-2026-53306/ (Markdown: https://insights.sbomify.com/CVE-2026-53306/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53306
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53306
- OSV: https://osv.dev/vulnerability/CVE-2026-53306

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53306/
Summaries are generated and may contain mistakes; the official description above is the record.