# CVE-2026-23243: RDMA/umad: Reject negative data_len in ib_umad_write

> A local attacker can trigger an integer overflow in the Linux kernel RDMA driver, leading to an out-of-bounds write and potential code execution or system crash.

- **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:** 18 Mar 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-80004, BELL-CVE-2026-23243, DEBIAN-CVE-2026-23243, GHSA-85rq-57vx-88q2, ROOT-OS-DEBIAN-11-CVE-2026-23243, ROOT-OS-DEBIAN-12-CVE-2026-23243, ROOT-OS-DEBIAN-13-CVE-2026-23243, ROOT-OS-UBUNTU-2204-CVE-2026-23243, ROOT-OS-UBUNTU-2404-CVE-2026-23243, UBUNTU-CVE-2026-23243

## What is CVE-2026-23243?

CVE-2026-23243 is a high-severity vulnerability in Linux kernel, published on 18 Mar 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:

RDMA/umad: Reject negative data_len in ib_umad_write

ib_umad_write computes data_len from user-controlled count and the
MAD header sizes. With a mismatched user MAD header size and RMPP
header length, data_len can become negative and reach ib_create_send_mad().
This can make the padding calculation exceed the segment size and trigger
an out-of-bounds memset in alloc_send_rmpp_list().

Add an explicit check to reject negative data_len before creating the
send buffer.

KASAN splat:
[  211.363464] BUG: KASAN: slab-out-of-bounds in ib_create_send_mad+0xa01/0x11b0
[  211.364077] Write of size 220 at addr ffff88800c3fa1f8 by task spray_thread/102
[  211.365867] ib_create_send_mad+0xa01/0x11b0
[  211.365887] ib_umad_write+0x853/0x1c80

Weakness: CWE-787 (Out-of-bounds Write), CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-23243?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23243?

Apply the vendor's patch.

## Is CVE-2026-23243 being exploited?

There is no known exploitation of CVE-2026-23243 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-2026-23243 and fix it if it is affected.

What it is: CVE-2026-23243 is a high-severity vulnerability in Linux kernel, published on 18 Mar 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-2026-23243 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-2026-23243/ (Markdown: https://insights.sbomify.com/CVE-2026-23243/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23243
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23243
- OSV: https://osv.dev/vulnerability/CVE-2026-23243

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23243/
Summaries are generated and may contain mistakes; the official description above is the record.