# What is CVE-2020-8927?

> CVE-2020-8927 is a medium-severity flaw (CVSS 6.5) in Brotli from Google, published on 15 September 2020. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 3.2%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2020-8927

## At a glance

- **Verdict:** Plan it in. No sign of exploitation and a low forecast. Patch it in your normal update cycle.
- **Precursor Intelligence risk score:** 33 out of 100 (Low); action: Monitor. Kept up to date as the evidence changes.
- **Severity:** Medium (CVSS 6.5 out of 10)
- **Known to be exploited:** No, not on the list of flaws known to be exploited today
- **Chance of use in the next 30 days:** 3.2% (latest exploit-likelihood forecast)
- **Published:** 15 September 2020
- **Record last updated:** 7 November 2023
- **Main product:** Brotli from Google
- **Affected products:** 10

## What is CVE-2020-8927? In plain terms

It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can change some data and slow it down.

### The official description

A buffer overflow exists in the Brotli library versions prior to 1.0.8 where an attacker controlling the input length of a "one-shot" decompression request to a script can trigger a crash, which happens when copying over chunks of data larger than 2 GiB. It is recommended to update your Brotli library to 1.0.8 or later. If one cannot update, we recommend to use the "streaming" API as opposed to the "one-shot" API, and impose chunk size limits.

### What kind of flaw is it?

- CWE-120: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
- CWE-130: Improper Handling of Length Parameter Inconsistency

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Easy: no special conditions
- Login needed first: No login needed
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can change some data and slow it down

Severity vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L`

## Is CVE-2020-8927 being exploited? Not that we know of

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 3.2%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 3.2%, 3.2%, 3.2%, 3.2%, 3.2%, 3.2%, 3.2%.

### Timeline

- 15 September 2020: Published
- 7 November 2023: Record last updated

### How Precursor Intelligence ranks it

CVE-2020-8927 scores **33 out of 100 (Low)**, with the action "Monitor".

Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less:

- Evidence it is being exploited: biggest factor
- How severe it is: strong factor
- How widely exposed it is: smaller factor
- Threat activity around it: smaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it.

## Who is affected by CVE-2020-8927?

The published record lists 10 products. Versions are as published: "before 1.0.8" means every version up to, but not including, 1.0.8.

- [Brotli](https://www.precursorintelligence.com/product/google/brotli) by [Google](https://www.precursorintelligence.com/vendors/google) (Application): before 1.0.8
- [Fedora](https://www.precursorintelligence.com/product/fedoraproject/fedora) by [Fedoraproject](https://www.precursorintelligence.com/vendors/fedoraproject) (Operating system): 31, 32, 33, 34, 35, 36
- [Powershell](https://www.precursorintelligence.com/product/microsoft/powershell) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Application): 7.0 to before 7.0.9, 7.1 to before 7.1.6, 7.2 to before 7.2.2
- [Ubuntu Linux](https://www.precursorintelligence.com/product/canonical/ubuntu_linux) by [Canonical](https://www.precursorintelligence.com/vendors/canonical) (Operating system): 16.04, 18.04, 20.04
- [Debian Linux](https://www.precursorintelligence.com/product/debian/debian_linux) by [Debian](https://www.precursorintelligence.com/vendors/debian) (Operating system): 9.0, 10.0
- [Visual Studio 2022](https://www.precursorintelligence.com/product/microsoft/visual_studio_2022) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Application): 17.0 to 17.0.7, 17.1
- .NET by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Application): 5.0 to 5.0.14
- .net Core by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Application): 3.1 to 3.1.22
- [Leap](https://www.precursorintelligence.com/product/opensuse/leap) by [Opensuse](https://www.precursorintelligence.com/vendors/opensuse) (Operating system): 15.2
- [Visual Studio 2019](https://www.precursorintelligence.com/product/microsoft/visual_studio_2019) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Application): 16.0 to 16.11

## How do I fix CVE-2020-8927?

1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
2. **Apply the vendor’s fix.** Install the latest update from the vendor. The references list where the vendor has published details.
3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.

### References

- [lists.opensuse.org](http://lists.opensuse.org/opensuse-security-announce/2020-09/msg00108.html) (Mailing list, Third-party advisory)
- [github.com](https://github.com/google/brotli/releases/tag/v1.0.9) (Release notes, Third-party advisory)
- [lists.debian.org](https://lists.debian.org/debian-lts-announce/2020/12/msg00003.html) (Mailing list, Third-party advisory)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/356JOYTWW4BWSZ42SEFLV7NYHL3S3AEH/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4TOGTZ2ZWDH662ZNFFSZVL3M5AJXV6JF/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/J4E265WKWKYMK2RYYSIXBEGZTDY5IQE6/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/M4VCDOJGL6BK3HB4XRD2WETBPYX2ITF6/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MMBKACMLSRX7JJSKBTR35UOEP2WFR6QP/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MQLM7ABVCYJLF6JRPF3M3EBXW63GNC27/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/W23CUADGMVMQQNFKHPHXVP7RPZJZNN6I/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WW62OZEY2GHJL4JCOLJRBSRETXDHMWRK/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZXEQ3GQVELA2T4HNZG7VPMS2HDVXMJRG/)
- [usn.ubuntu.com](https://usn.ubuntu.com/4568-1/) (Third-party advisory)
- [debian.org](https://www.debian.org/security/2020/dsa-4801) (Third-party advisory)

## Questions

### What is CVE-2020-8927?

CVE-2020-8927 is a medium-severity flaw in Brotli from Google, published on 15 September 2020. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can change some data and slow it down.

### How serious is CVE-2020-8927?

It scores 6.5 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2020-8927 is 33 out of 100, which is Low. Its action is "Monitor". No sign of exploitation and a low forecast. Patch it in your normal update cycle.

### Is CVE-2020-8927 being exploited?

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 3.2%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2020-8927 affect?

For Brotli from Google: before 1.0.8. The record lists 10 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2020-8927?

Install the update the vendor names in its advisory. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

## Does CVE-2020-8927 affect you?

Precursor Intelligence keeps checking for you:

- **Tell us what you run.** Pick your software from a list, or let us work it out from your website.
- **We match it to every flaw.** Over 400,000 published flaws, checked against your list.
- **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it.
- **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools.

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