# CVE-2019-15793: Mishandling of file-system uid/gid with namespaces in shiftfs

> A local attacker can bypass discretionary access control permissions in Ubuntu kernels due to incorrect user/group ID translation in shiftfs.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N`)
- **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:** 23 Apr 2020
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-h5g7-x752-wjh8, UBUNTU-CVE-2019-15793

## What is CVE-2019-15793?

CVE-2019-15793 is a medium-severity authentication bypass vulnerability in Canonical Ubuntu Linux, published on 23 Apr 2020. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In shiftfs, a non-upstream patch to the Linux kernel included in the Ubuntu 5.0 and 5.3 kernel series, several locations which shift ids translate user/group ids before performing operations in the lower filesystem were translating them into init_user_ns, whereas they should have been translated into the s_user_ns for the lower filesystem. This resulted in using ids other than the intended ones in the lower fs, which likely did not map into the shifts s_user_ns. A local attacker could use this to possibly bypass discretionary access control permissions.

Weakness: CWE-276 (Incorrect Default Permissions), CWE-538 (Insertion of Sensitive Information into Externally-Accessible File or Directory)

## Which versions are affected by CVE-2019-15793?

It affects 2 products.


Products: Canonical Ubuntu Linux, Linux kernel.

## How do I fix CVE-2019-15793?

Apply the vendor's patch.

## Is CVE-2019-15793 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-15793 exists.

Public exploit code:

- Ubuntu 19.10 - Refcount Underflow and Type Confusion in shiftfs (exploitdb)

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2020-11651](https://insights.sbomify.com/CVE-2020-11651/): SaltStack Salt Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2020-7247](https://insights.sbomify.com/CVE-2020-7247/): OpenSMTPD Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2019-16928](https://insights.sbomify.com/CVE-2019-16928/): Exim Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2018-6789](https://insights.sbomify.com/CVE-2018-6789/): Exim Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2015-2590](https://insights.sbomify.com/CVE-2015-2590/): Oracle Java SE and Java SE Embedded Remote Code Execution (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-15793 and fix it if it is affected.

What it is: CVE-2019-15793 is a medium-severity authentication bypass vulnerability in Canonical Ubuntu Linux, published on 23 Apr 2020. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-15793 exists.

Affected product: Canonical Ubuntu 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-2019-15793/ (Markdown: https://insights.sbomify.com/CVE-2019-15793/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-15793
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-15793
- OSV: https://osv.dev/vulnerability/CVE-2019-15793

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From sbomify Insights: https://insights.sbomify.com/CVE-2019-15793/
Summaries are generated and may contain mistakes; the official description above is the record.