# CVE-2020-28327: Race condition in n/a

> An authenticated remote attacker can crash Asterisk via a race condition in SIP session handling when using TCP or TLS transport.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Nov 2020
- **Updated:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2020-28327, DEBIAN-CVE-2020-28327, GHSA-ggx6-v629-c48v, UBUNTU-CVE-2020-28327

## What is CVE-2020-28327?

CVE-2020-28327 is a medium-severity vulnerability in Digium Certified Asterisk, published on 6 Nov 2020. Any signed-in user can exploit it over the network, with no action from the victim.

### 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.

Weakness: CWE-404 (Improper Resource Shutdown or Release)

## Which versions are affected by CVE-2020-28327?

It affects 2 products.


Products: Digium Certified Asterisk, Sangoma Asterisk.

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

Upgrade to a fixed version.

## Is CVE-2020-28327 being exploited?

There is no known exploitation of CVE-2020-28327 in the wild and no public exploit code.

## Other vulnerabilities in Digium Certified Asterisk

- [CVE-2017-9359](https://insights.sbomify.com/CVE-2017-9359/): Denial of service in n/a (high 7.5)
- [CVE-2017-9372](https://insights.sbomify.com/CVE-2017-9372/): Memory corruption in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-28327 and fix it if it is affected.

What it is: CVE-2020-28327 is a medium-severity vulnerability in Digium Certified Asterisk, published on 6 Nov 2020. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2020-28327 in the wild and no public exploit code.

Affected product: Digium Certified Asterisk. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2020-28327/ (Markdown: https://insights.sbomify.com/CVE-2020-28327/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-28327
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-28327
- OSV: https://osv.dev/vulnerability/CVE-2020-28327

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-28327/
Summaries are generated and may contain mistakes; the official description above is the record.