# CVE-2021-46837: Null dereference in n/a

> An attacker can crash the Asterisk PBX by sending a malformed T.38 re-invite response, causing a denial of service.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/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:** 30 Aug 2022
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-46837, GHSA-544v-7w28-m77x, UBUNTU-CVE-2021-46837

## What is CVE-2021-46837?

CVE-2021-46837 is a medium-severity vulnerability in Debian Debian Linux, published on 30 Aug 2022. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

res_pjsip_t38 in Sangoma Asterisk 16.x before 16.16.2, 17.x before 17.9.3, and 18.x before 18.2.2, and Certified Asterisk before 16.8-cert7, allows an attacker to trigger a crash by sending an m=image line and zero port in a response to a T.38 re-invite initiated by Asterisk. This is a re-occurrence of the CVE-2019-15297 symptoms but not for exactly the same reason. The crash occurs because there is an append operation relative to the active topology, but this should instead be a replace operation.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2021-46837?

It affects 3 products.


Products: Asterisk Certified Asterisk, Debian Debian Linux, Digium Asterisk.

## How do I fix CVE-2021-46837?

Upgrade to a fixed version.

## Is CVE-2021-46837 being exploited?

There is no known exploitation of CVE-2021-46837 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2022-21723](https://insights.sbomify.com/CVE-2022-21723/): Out-of-bounds read in multipart parsing in PJSIP (critical 9.1)
- [CVE-2022-23608](https://insights.sbomify.com/CVE-2022-23608/): Use after free in PJSIP (high 8.1)
- [CVE-2017-9358](https://insights.sbomify.com/CVE-2017-9358/): Denial of service in n/a (high 7.5)
- [CVE-2021-37706](https://insights.sbomify.com/CVE-2021-37706/): Potential integer underflow upon receiving STUN message in PJSIP (high 7.3)
- [CVE-2020-28242](https://insights.sbomify.com/CVE-2020-28242/): Denial of service in n/a (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-46837 and fix it if it is affected.

What it is: CVE-2021-46837 is a medium-severity vulnerability in Debian Debian Linux, published on 30 Aug 2022. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-46837 in the wild and no public exploit code.

Affected product: Debian Debian Linux. 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-2021-46837/ (Markdown: https://insights.sbomify.com/CVE-2021-46837/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-46837
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-46837
- OSV: https://osv.dev/vulnerability/CVE-2021-46837

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-46837/
Summaries are generated and may contain mistakes; the official description above is the record.