# CVE-2016-2856: Privilege escalation in n/a

> Local attackers can capture keystrokes and potentially gain privileges via pt_chown if the non-default --enable-pt_chown option is enabled in glibc.

- **Severity:** High 8.4 (`CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 14 Mar 2016
- **Updated:** 5 Aug 2024
- **Also known as:** DEBIAN-CVE-2016-2856, GHSA-2wf2-64hh-9h2m, UBUNTU-CVE-2016-2856

## What is CVE-2016-2856?

CVE-2016-2856 is a high-severity vulnerability in Canonical Ubuntu Linux, published on 14 Mar 2016. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

pt_chown in the glibc package before 2.19-18+deb8u4 on Debian jessie; the elibc package before 2.15-0ubuntu10.14 on Ubuntu 12.04 LTS and before 2.19-0ubuntu6.8 on Ubuntu 14.04 LTS; and the glibc package before 2.21-0ubuntu4.2 on Ubuntu 15.10 and before 2.23-0ubuntu1 on Ubuntu 16.04 LTS and 16.10 lacks a namespace check associated with file-descriptor passing, which allows local users to capture keystrokes and spoof data, and possibly gain privileges, via pts read and write operations, related to debian/sysdeps/linux.mk.  NOTE: this is not considered a vulnerability in the upstream GNU C Library because the upstream documentation has a clear security recommendation against the --enable-pt_chown option.

Weakness: CWE-264

## Which versions are affected by CVE-2016-2856?

It affects 2 products.


Products: Canonical Ubuntu Linux, Debian Debian Linux.

## How do I fix CVE-2016-2856?

Apply the vendor's patch.

## Is CVE-2016-2856 being exploited?

There is no known exploitation of CVE-2016-2856 in the wild and no public exploit code.

Public exploit code:

- Ubuntu < 15.10 - PT Chown Arbitrary PTs Access Via User Namespace Privilege Escalation (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-2016-2856 and fix it if it is affected.

What it is: CVE-2016-2856 is a high-severity vulnerability in Canonical Ubuntu Linux, published on 14 Mar 2016. 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-2016-2856 in the wild and no public exploit code.

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-2016-2856/ (Markdown: https://insights.sbomify.com/CVE-2016-2856/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2016-2856
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2016-2856
- OSV: https://osv.dev/vulnerability/CVE-2016-2856

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From sbomify Insights: https://insights.sbomify.com/CVE-2016-2856/
Summaries are generated and may contain mistakes; the official description above is the record.