# What is CVE-2020-28327?

> CVE-2020-28327 is a medium-severity flaw (CVSS 5.3) in Certified Asterisk from Digium, published on 6 November 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 1.9%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2020-28327

## 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:** 40 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** Medium (CVSS 5.3 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:** 1.9% (latest exploit-likelihood forecast)
- **Published:** 6 November 2020
- **Record last updated:** 15 August 2024
- **Main product:** Certified Asterisk from Digium
- **Affected products:** 2

## What is CVE-2020-28327? In plain terms

It can be attacked from anywhere on the internet with an ordinary user account, and nobody has to click anything. If it works, the attacker can take it offline.

### The official description

A res_pjsip_session crash was discovered in Asterisk Open Source 13.x before 13.37.1, 16.x before 16.14.1, 17.x before 17.8.1, and 18.x before 18.0.1. and Certified Asterisk before 16.8-cert5. Upon receiving a new SIP Invite, Asterisk did not return the created dialog locked or referenced. This caused a gap between the creation of the dialog object, and its next use by the thread that created it. Depending on some off-nominal circumstances and timing, it was possible for another thread to free said dialog in this gap. Asterisk could then crash when the dialog object, or any of its dependent objects, were dereferenced or accessed next by the initial-creation thread. Note, however, that this crash can only occur when using a connection-oriented protocol (e.g., TCP or TLS, but not UDP) for SIP transport. Also, the remote client must be authenticated, or Asterisk must be configured for anonymous calling.

### What kind of flaw is it?

- CWE-404: Improper Resource Shutdown or Release

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Hard: conditions must line up
- Login needed first: An ordinary user account
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can take it offline

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

## Is CVE-2020-28327 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 1.9%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 1.9%, 1.9%, 1.9%, 1.9%, 1.9%, 1.9%, 1.9%.

### Timeline

- 6 November 2020: Published
- 15 August 2024: Record last updated

### How Precursor Intelligence ranks it

CVE-2020-28327 scores **40 out of 100 (Medium)**, with the action "Plan remediation".

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: key context
- Real threat activity around it: key context

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-2020-28327?

The published record lists 2 products. Versions are as published: "13.0.0 to before 13.37.1" means from 13.0.0 up to, but not including, 13.37.1.

- [Certified Asterisk](https://www.precursorintelligence.com/product/digium/certified_asterisk) by [Digium](https://www.precursorintelligence.com/vendors/digium) (Application): 16.8, 16.8-cert1-rc1, 16.8-cert1-rc2, 16.8-cert1-rc3, 16.8-cert1-rc4, 16.8-cert2, 16.8-cert3, 16.8-cert4-rc1, 16.8-cert4-rc2, 16.8-cert4-rc3, 16.8-cert4-rc4, 16.8-cert4
- [Asterisk](https://www.precursorintelligence.com/product/sangoma/asterisk) by [Sangoma](https://www.precursorintelligence.com/vendors/sangoma) (Application): 13.0.0 to before 13.37.1, 16.0.0 to before 16.14.1, 17.0.0 to before 17.8.1, 18.0.0 to before 18.0.1

## How do I fix CVE-2020-28327?

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 update named in the vendor’s advisory. We’ve put the advisories and patch notes first in the list.
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

- [downloads.asterisk.org](http://downloads.asterisk.org/pub/security/AST-2020-001.html) (Patch, Vendor advisory)
- [issues.asterisk.org](https://issues.asterisk.org/jira/browse/ASTERISK-29057) (Exploit, Issue tracking, Vendor advisory)

## Questions

### What is CVE-2020-28327?

CVE-2020-28327 is a medium-severity flaw in Certified Asterisk from Digium, published on 6 November 2020. It can be attacked from anywhere on the internet with an ordinary user account, and nobody has to click anything. If it works, the attacker can take it offline.

### How serious is CVE-2020-28327?

It scores 5.3 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2020-28327 is 40 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle.

### Is CVE-2020-28327 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 1.9%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2020-28327 affect?

For Certified Asterisk from Digium: 16.8, 16.8-cert1-rc1, 16.8-cert1-rc2, 16.8-cert1-rc3, 16.8-cert1-rc4, 16.8-cert2 and 6 more. The record lists 2 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2020-28327?

Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

## Does CVE-2020-28327 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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