# CVE-2021-3864: Privilege escalation in kernel

> An unprivileged local user can escalate privileges by exploiting SUID binary core dump handling when core_pattern is relative.

- **Severity:** High 7.0 (`CVSS:3.1/AV:L/AC:H/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:** 26 Aug 2022
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3864, GHSA-9682-f2fr-3h46, ROOT-OS-DEBIAN-11-CVE-2021-3864, ROOT-OS-DEBIAN-12-CVE-2021-3864, ROOT-OS-DEBIAN-13-CVE-2021-3864, ROOT-OS-UBUNTU-2204-CVE-2021-3864, ROOT-OS-UBUNTU-2404-CVE-2021-3864, UBUNTU-CVE-2021-3864

## What is CVE-2021-3864?

CVE-2021-3864 is a high-severity vulnerability in Debian Debian Linux, published on 26 Aug 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A flaw was found in the way the dumpable flag setting was handled when certain SUID binaries executed its descendants. The prerequisite is a SUID binary that sets real UID equal to effective UID, and real GID equal to effective GID. The descendant will then have a dumpable value set to 1. As a result, if the descendant process crashes and core_pattern is set to a relative value, its core dump is stored in the current directory with uid:gid permissions. An unprivileged local user with eligible root SUID binary could use this flaw to place core dumps into root-owned directories, potentially resulting in escalation of privileges.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2021-3864?

It affects 3 products.


Products: Debian Debian Linux, Linux kernel, Redhat Enterprise Linux.

## How do I fix CVE-2021-3864?

Apply the vendor's patch.

## Is CVE-2021-3864 being exploited?

There is no known exploitation of CVE-2021-3864 in the wild and no public exploit code.

Public exploit code:

- Test for cve-2021-3864 (github_poc): https://github.com/walac/cve-2021-3864

## 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-2021-3864 and fix it if it is affected.

What it is: CVE-2021-3864 is a high-severity vulnerability in Debian Debian Linux, published on 26 Aug 2022. 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-2021-3864 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-2021-3864/ (Markdown: https://insights.sbomify.com/CVE-2021-3864/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3864
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3864
- OSV: https://osv.dev/vulnerability/CVE-2021-3864

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3864/
Summaries are generated and may contain mistakes; the official description above is the record.