---
title: "CVE-2016-6354\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2016-6354?format=md
keywords: index, follow
---

# CVE-2016-6354

Publication date 21 September 2016

Last updated 26 August 2025

---

Ubuntu priority

**Low**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**9.8 · Critical**

[Score breakdown](https://ubuntu.com/security/CVE-2016-6354?format=md#impact-score)

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## Description

Heap-based buffer overflow in the yy\_get\_next\_buffer function in Flex
before 2.6.1 might allow context-dependent attackers to cause a denial of
service or possibly execute arbitrary code via vectors involving
num\_to\_read.

[Read the notes from the security team](https://ubuntu.com/security/CVE-2016-6354?format=md#notes)

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| flex | 26.04 LTS resolute | Not affected |
| 25.10 questing | Not affected |
| 25.04 plucky | Not affected |
| 24.10 oracular | Not affected |
| 24.04 LTS noble | Not affected |
| 23.10 mantic | Not affected |
| 23.04 lunar | Not affected |
| 22.10 kinetic | Not affected |
| 22.04 LTS jammy | Not affected |
| 21.10 impish | Not affected |
| 21.04 hirsute | Not affected |
| 20.10 groovy | Not affected |
| 20.04 LTS focal | Not affected |
| 19.10 eoan | Not affected |
| 19.04 disco | Not affected |
| 18.10 cosmic | Not affected |
| 18.04 LTS bionic | Not affected |
| 17.10 artful | Not affected |
| 17.04 zesty | Not affected |
| 16.10 yakkety | Not affected |
| 16.04 LTS xenial | Vulnerable |
| 15.10 wily | Ignored end of life |
| 14.04 LTS trusty | Not in release |
| 12.04 LTS precise | Not affected |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)
* [Patch details](https://ubuntu.com/security/CVE-2016-6354?format=md#patch-details)

## Notes

---

### [mdeslaur](https://launchpad.net/~mdeslaur)

introduced in 2.5.36 by
https://github.com/westes/flex/commit/9ba3187a537d6a58d345f2874d06087fd4050399

---

### [sbeattie](https://launchpad.net/~sbeattie)

redhat bug claims that it's not exploitable due to followup code
also, simply replacing yy\_size\_t with int on num\_to\_read as
in the upstream patch causes even more signed comparison warnings in
flex generated sources; there's a comparison against a size\_t
variable in YY\_INPUT for one. The "correct" fix for this likely includes
the additional commit mentioned in the oss-security post.
fixing will also require recompiling anything with generated
code from the versions of flex in vivid through xenial.

### Patch details

For informational purposes only. We recommend not to cherry-pick updates. [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)

| Package | Patch details |
| --- | --- |
| flex | * Upstream:   [a5cbe92](https://github.com/westes/flex/commit/a5cbe929ac3255d371e698f62dc256afe7006466) |

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

9.8 · Critical

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Privileges required | None |
  | User interaction | None |
  | Scope | Unchanged |
  | Confidentiality impact | High |
  | Integrity impact | High |
  | Availability impact | High |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 9.8 · Critical |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-6354)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2016-6354)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2016-6354)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2016-6354)

### Other references

* <http://seclists.org/oss-sec/2016/q3/97>
* <https://www.cve.org/CVERecord?id=CVE-2016-6354>