---
title: "CVE-2021-36740\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-2021-36740?format=md
keywords: index, follow
---

# CVE-2021-36740

Publication date 14 July 2021

Last updated 25 August 2025

---

Ubuntu priority

**Medium**

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

## Cvss 3 Severity Score

**6.5 · Medium**

[Score breakdown](https://ubuntu.com/security/CVE-2021-36740?format=md#impact-score)

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## Description

Varnish Cache, with HTTP/2 enabled, allows request smuggling and VCL
authorization bypass via a large Content-Length header for a POST request.
This affects Varnish Enterprise 6.0.x before 6.0.8r3, and Varnish Cache 5.x
and 6.x before 6.5.2, 6.6.x before 6.6.1, and 6.0 LTS before 6.0.8.

[Read the notes from the security team](https://ubuntu.com/security/CVE-2021-36740?format=md#notes)

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| varnish | 22.04 LTS jammy | Not affected |
| 21.10 impish | Fixed 6.5.2-1 |
| 21.04 hirsute | Ignored end of life |
| 20.10 groovy | Ignored end of life |
| 20.04 LTS focal | Fixed 6.2.1-2ubuntu0.1 |
| 18.04 LTS bionic | Not affected |
| 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)

## Notes

---

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

According to Debian:
(HTTP/2 support is marked experimental in 5.0 and enabling is not
recommended, code is quite different)

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

6.5 · Medium

* Base metrics

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

  | Parameter | Value |
  | --- | --- |
  | Base score | 6.5 · Medium |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-36740)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2021-36740)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2021-36740)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2021-36740)

### Related Ubuntu Security Notices (USN)

+ [USN-5474-1](https://usn.ubuntu.com/USN-5474-1)
+ Varnish Cache vulnerabilities
+ 8 June 2022

### Other references

* <https://varnish-cache.org/security/VSV00007.html>
* <https://github.com/varnishcache/varnish-cache/commit/9be22198e258d0e7a5c41f4291792214a29405cf (6.0.8)>
* <https://github.com/varnishcache/varnish-cache/commit/82b0a629f60136e76112c6f2c6372cce77b683be (6.5.2)>
* <https://github.com/varnishcache/varnish-cache/commit/82b0a629f60136e76112c6f2c6372cce77b683be>
* <https://github.com/varnishcache/varnish-cache/commit/9be22198e258d0e7a5c41f4291792214a29405cf>
* <https://docs.varnish-software.com/security/VSV00007/>
* <https://www.cve.org/CVERecord?id=CVE-2021-36740>