# CVE-2026-43492: lib/crypto: mpi: Fix integer underflow in mpi_read_raw_from_sgl()

> An integer underflow in the Linux kernel's MPI library allows local attackers to cause a denial of service via a system call.

- **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:** 19 May 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-86975, BELL-CVE-2026-43492, DEBIAN-CVE-2026-43492, GHSA-q8fh-4v85-p8mj, ROOT-OS-DEBIAN-11-CVE-2026-43492, ROOT-OS-DEBIAN-12-CVE-2026-43492, ROOT-OS-UBUNTU-2204-CVE-2026-43492, ROOT-OS-UBUNTU-2404-CVE-2026-43492, UBUNTU-CVE-2026-43492

## What is CVE-2026-43492?

CVE-2026-43492 is a medium-severity vulnerability in Linux kernel, published on 19 May 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:

lib/crypto: mpi: Fix integer underflow in mpi_read_raw_from_sgl()

Yiming reports an integer underflow in mpi_read_raw_from_sgl() when
subtracting "lzeros" from the unsigned "nbytes".

For this to happen, the scatterlist "sgl" needs to occupy more bytes
than the "nbytes" parameter and the first "nbytes + 1" bytes of the
scatterlist must be zero.  Under these conditions, the while loop
iterating over the scatterlist will count more zeroes than "nbytes",
subtract the number of zeroes from "nbytes" and cause the underflow.

When commit 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers") originally
introduced the bug, it couldn't be triggered because all callers of
mpi_read_raw_from_sgl() passed a scatterlist whose length was equal to
"nbytes".

However since commit 63ba4d67594a ("KEYS: asymmetric: Use new crypto
interface without scatterlists"), the underflow can now actually be
triggered.  When invoking a KEYCTL_PKEY_ENCRYPT system call with a
larger "out_len" than "in_len" and filling the "in" buffer with zeroes,
crypto_akcipher_sync_prep() will create an all-zero scatterlist used for
both the "src" and "dst" member of struct akcipher_request and thereby
fulfil the conditions to trigger the bug:

  sys_keyctl()
    keyctl_pkey_e_d_s()
      asymmetric_key_eds_op()
        software_key_eds_op()
          crypto_akcipher_sync_encrypt()
            crypto_akcipher_sync_prep()
              crypto_akcipher_encrypt()
                rsa_enc()
                  mpi_read_raw_from_sgl()

To the user this will be visible as a DoS as the kernel spins forever,
causing soft lockup splats as a side effect.

Fix it.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-43492?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43492?

Apply the vendor's patch.

## Is CVE-2026-43492 being exploited?

There is no known exploitation of CVE-2026-43492 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-2026-43492 and fix it if it is affected.

What it is: CVE-2026-43492 is a medium-severity vulnerability in Linux kernel, published on 19 May 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-2026-43492 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-2026-43492/ (Markdown: https://insights.sbomify.com/CVE-2026-43492/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43492
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43492
- OSV: https://osv.dev/vulnerability/CVE-2026-43492

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43492/
Summaries are generated and may contain mistakes; the official description above is the record.