# CVE-2021-26717: Denial of service in n/a

> A remote attacker can cause a denial of service in Asterisk by delaying T.38 re-negotiation responses, leading to a crash.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** ALPINE-CVE-2021-26717, DEBIAN-CVE-2021-26717, GHSA-9mrj-wq9r-h4vw, UBUNTU-CVE-2021-26717

## What is CVE-2021-26717?

CVE-2021-26717 is a high-severity denial of service vulnerability in Digium Asterisk, published on 18 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An issue was discovered in Sangoma Asterisk 16.x before 16.16.1, 17.x before 17.9.2, and 18.x before 18.2.1 and Certified Asterisk before 16.8-cert6. When re-negotiating for T.38, if the initial remote response was delayed just enough, Asterisk would send both audio and T.38 in the SDP. If this happened, and the remote responded with a declined T.38 stream, then Asterisk would crash.

## Which versions are affected by CVE-2021-26717?

It affects 2 products.


Products: Digium Asterisk, Digium Certified Asterisk.

## How do I fix CVE-2021-26717?

Upgrade to a fixed version.

## Is CVE-2021-26717 being exploited?

There is no known exploitation of CVE-2021-26717 in the wild and no public exploit code.

## Other vulnerabilities in Digium Asterisk

- [CVE-2017-14100](https://insights.sbomify.com/CVE-2017-14100/): Command injection in n/a (critical 9.8)
- [CVE-2014-8418](https://insights.sbomify.com/CVE-2014-8418/): Privilege escalation in n/a (critical 9.0)
- [CVE-2011-1599](https://insights.sbomify.com/CVE-2011-1599/): Missing authorization in n/a (critical 9.0)
- [CVE-2017-16671](https://insights.sbomify.com/CVE-2017-16671/): Memory corruption in n/a (high 8.8)
- [CVE-2017-7617](https://insights.sbomify.com/CVE-2017-7617/): Memory corruption in n/a (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-26717 and fix it if it is affected.

What it is: CVE-2021-26717 is a high-severity denial of service vulnerability in Digium Asterisk, published on 18 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-26717 in the wild and no public exploit code.

Affected product: Digium 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-2021-26717/ (Markdown: https://insights.sbomify.com/CVE-2021-26717/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-26717
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-26717
- OSV: https://osv.dev/vulnerability/CVE-2021-26717

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-26717/
Summaries are generated and may contain mistakes; the official description above is the record.