# CVE-2021-47182: scsi: core: Fix scsi_mode_sense() buffer length handling

> A buffer handling flaw in the Linux kernel SCSI subsystem allows memory corruption, potentially leading to code execution or privilege escalation.

- **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:** 10 Apr 2024
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2021-47182, GHSA-qq35-93pf-cxxv, ROOT-OS-DEBIAN-11-CVE-2021-47182, UBUNTU-CVE-2021-47182

## What is CVE-2021-47182?

CVE-2021-47182 is a medium-severity memory corruption vulnerability in Linux kernel, published on 10 Apr 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:

scsi: core: Fix scsi_mode_sense() buffer length handling

Several problems exist with scsi_mode_sense() buffer length handling:

 1) The allocation length field of the MODE SENSE(10) command is 16-bits,
    occupying bytes 7 and 8 of the CDB. With this command, access to mode
    pages larger than 255 bytes is thus possible. However, the CDB
    allocation length field is set by assigning len to byte 8 only, thus
    truncating buffer length larger than 255.

 2) If scsi_mode_sense() is called with len smaller than 8 with
    sdev->use_10_for_ms set, or smaller than 4 otherwise, the buffer length
    is increased to 8 and 4 respectively, and the buffer is zero filled
    with these increased values, thus corrupting the memory following the
    buffer.

Fix these 2 problems by using put_unaligned_be16() to set the allocation
length field of MODE SENSE(10) CDB and by returning an error when len is
too small.

Furthermore, if len is larger than 255B, always try MODE SENSE(10) first,
even if the device driver did not set sdev->use_10_for_ms. In case of
invalid opcode error for MODE SENSE(10), access to mode pages larger than
255 bytes are not retried using MODE SENSE(6). To avoid buffer length
overflows for the MODE_SENSE(10) case, check that len is smaller than 65535
bytes.

While at it, also fix the folowing:

 * Use get_unaligned_be16() to retrieve the mode data length and block
   descriptor length fields of the mode sense reply header instead of using
   an open coded calculation.

 * Fix the kdoc dbd argument explanation: the DBD bit stands for Disable
   Block Descriptor, which is the opposite of what the dbd argument
   description was.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2021-47182?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47182?

Apply the vendor's patch.

## Is CVE-2021-47182 being exploited?

There is no known exploitation of CVE-2021-47182 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-2021-47182 and fix it if it is affected.

What it is: CVE-2021-47182 is a medium-severity memory corruption vulnerability in Linux kernel, published on 10 Apr 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-2021-47182 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-2021-47182/ (Markdown: https://insights.sbomify.com/CVE-2021-47182/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47182
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47182
- OSV: https://osv.dev/vulnerability/CVE-2021-47182

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47182/
Summaries are generated and may contain mistakes; the official description above is the record.