# CVE-2021-32686: Denial of Service in PJSIP

> A race condition in PJSIP SSL sockets causes crashes under heavy TLS load, leading to denial of service for applications using the library.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/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:** 23 Jul 2021
- **Updated:** 4 Nov 2025
- **Also known as:** ALPINE-CVE-2021-32686, DEBIAN-CVE-2021-32686, GHSA-cv8x-p47p-99wr, MGASA-2021-0559, UBUNTU-CVE-2021-32686

## What is CVE-2021-32686?

CVE-2021-32686 is a medium-severity vulnerability in Debian Debian Linux, published on 23 Jul 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 PJSIP before version 2.11.1, there are a couple of issues found in the SSL socket. First, a race condition between callback and destroy, due to the accepted socket having no group lock. Second, the SSL socket parent/listener may get destroyed during handshake. Both issues were reported to happen intermittently in heavy load TLS connections. They cause a crash, resulting in a denial of service. These are fixed in version 2.11.1.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2021-32686?

It affects 2 products.


Products: Debian Debian Linux, Teluu Pjsip.

## How do I fix CVE-2021-32686?

Upgrade to a fixed version.

## Is CVE-2021-32686 being exploited?

There is no known exploitation of CVE-2021-32686 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-32686 and fix it if it is affected.

What it is: CVE-2021-32686 is a medium-severity vulnerability in Debian Debian Linux, published on 23 Jul 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-2021-32686 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-2021-32686/ (Markdown: https://insights.sbomify.com/CVE-2021-32686/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32686
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32686
- OSV: https://osv.dev/vulnerability/CVE-2021-32686

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32686/
Summaries are generated and may contain mistakes; the official description above is the record.