# CVE-2021-37706: Potential integer underflow upon receiving STUN message in PJSIP

> A malicious actor can trigger an integer underflow in PJSIP via crafted STUN messages, leading to remote arbitrary code execution.

- **Severity:** High 7.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Dec 2021
- **Updated:** 4 Nov 2025
- **Also known as:** ALPINE-CVE-2021-37706, DEBIAN-CVE-2021-37706, GHSA-2qpg-f6wf-w984, UBUNTU-CVE-2021-37706

## What is CVE-2021-37706?

CVE-2021-37706 is a high-severity vulnerability in Debian Debian Linux, published on 22 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

PJSIP is a free and open source multimedia communication library written in C language implementing standard based protocols such as SIP, SDP, RTP, STUN, TURN, and ICE. In affected versions if the incoming STUN message contains an ERROR-CODE attribute, the header length is not checked before performing a subtraction operation, potentially resulting in an integer underflow scenario. This issue affects all users that use STUN. A malicious actor located within the victim’s network may forge and send a specially crafted UDP (STUN) message that could remotely execute arbitrary code on the victim’s machine. Users are advised to upgrade as soon as possible. There are no known workarounds.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2021-37706?

It affects 4 products.


Products: Asterisk Certified Asterisk, Debian Debian Linux, Sangoma Asterisk, Teluu Pjsip.

## How do I fix CVE-2021-37706?

Upgrade to a fixed version.

## Is CVE-2021-37706 being exploited?

There is no known exploitation of CVE-2021-37706 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-2021-46837](https://insights.sbomify.com/CVE-2021-46837/): Null dereference in n/a (medium 6.5)
- [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-2021-37706 and fix it if it is affected.

What it is: CVE-2021-37706 is a high-severity vulnerability in Debian Debian Linux, published on 22 Dec 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-2021-37706 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-2021-37706/ (Markdown: https://insights.sbomify.com/CVE-2021-37706/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-37706
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-37706
- OSV: https://osv.dev/vulnerability/CVE-2021-37706

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-37706/
Summaries are generated and may contain mistakes; the official description above is the record.