---
title: "CVE-2019-8955\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-2019-8955?format=md
keywords: index, follow
---

# CVE-2019-8955

Publication date 21 February 2019

Last updated 25 August 2025

---

Ubuntu priority

**Medium**

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

## Cvss 3 Severity Score

**7.5 · High**

[Score breakdown](https://ubuntu.com/security/CVE-2019-8955?format=md#impact-score)

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## Description

In Tor before 0.3.3.12, 0.3.4.x before 0.3.4.11, 0.3.5.x before 0.3.5.8,
and 0.4.x before 0.4.0.2-alpha, remote denial of service against Tor
clients and relays can occur via memory exhaustion in the KIST cell
scheduler.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| tor | 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 | Ignored end of life |
| 18.04 LTS bionic | Fixed 0.3.2.10-1ubuntu0.2~esm1  Ubuntu Pro |
| 16.04 LTS xenial | Not affected |
| 14.04 LTS trusty | 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-2019-8955?format=md#patch-details)

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### 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 |
| --- | --- |
| tor | * Upstream:   [be84ed1](https://github.com/torproject/tor/commit/be84ed1a64ed7ce810bd3924fa96c2588b491ef5) |

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

7.5 · High

* Base metrics

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

  | Parameter | Value |
  | --- | --- |
  | Base score | 7.5 · High |
  | Exploitability score | - |
  | Impact score | - |

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

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-8955)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2019-8955)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2019-8955)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2019-8955)

### Related Ubuntu Security Notices (USN)

+ [USN-5036-1](https://usn.ubuntu.com/USN-5036-1)
+ Tor vulnerabilities
+ 4 October 2022

### Other references

* <https://blog.torproject.org/new-releases-tor-0402-alpha-0358-03411-and-03312>
* <https://trac.torproject.org/projects/tor/ticket/29168>
* <https://www.cve.org/CVERecord?id=CVE-2019-8955>