# CVE-2021-28688: Memory corruption in Linux

> A regression in the Linux kernel's Xen grant table cleanup logic causes resource leaks and zombie domains, leading to denial of service and potential information disclosure.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/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:** 6 Apr 2021
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-28688, GHSA-hqhv-rx9w-cr56, SUSE-SU-2021:1341-1, SUSE-SU-2022:1003-1, UBUNTU-CVE-2021-28688

## What is CVE-2021-28688?

CVE-2021-28688 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 6 Apr 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

The fix for XSA-365 includes initialization of pointers such that subsequent cleanup code wouldn't use uninitialized or stale values. This initialization went too far and may under certain conditions also overwrite pointers which are in need of cleaning up. The lack of cleanup would result in leaking persistent grants. The leak in turn would prevent fully cleaning up after a respective guest has died, leaving around zombie domains. All Linux versions having the fix for XSA-365 applied are vulnerable. XSA-365 was classified to affect versions back to at least 3.11.

Weakness: CWE-665 (Improper Initialization)

## Which versions are affected by CVE-2021-28688?

It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `kgraft-patch-SLE12-SP3_Update_38` | SUSE:Linux Enterprise Server 12 SP3-LTSS | All versions | 3-2.2 |
| `kgraft-patch-SLE12-SP3_Update_43` | SUSE:Linux Enterprise Server 12 SP3-LTSS | All versions | 2-2.1 |
| `kgraft-patch-SLE12-SP3_Update_38` | SUSE:Linux Enterprise Server for SAP Applications 12 SP3 | All versions | 3-2.2 |
| `kgraft-patch-SLE12-SP3_Update_43` | SUSE:Linux Enterprise Server for SAP Applications 12 SP3 | All versions | 2-2.1 |

Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2021-28688?

Apply the vendor's patch.

## Is CVE-2021-28688 being exploited?

There is no known exploitation of CVE-2021-28688 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-28688 and fix it if it is affected.

What it is: CVE-2021-28688 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 6 Apr 2021. 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-2021-28688 in the wild and no public exploit code.

Affected product: Debian Debian 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-2021-28688/ (Markdown: https://insights.sbomify.com/CVE-2021-28688/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-28688
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-28688
- OSV: https://osv.dev/vulnerability/CVE-2021-28688

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-28688/
Summaries are generated and may contain mistakes; the official description above is the record.