# CVE-2021-41157: FreeSWITCH does not authenticate SIP SUBSCRIBE requests by default

> Attackers can subscribe to user agent event notifications without authentication, allowing them to monitor SIP extension status and potentially facilitate social engineering attacks.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Oct 2021
- **Updated:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2021-41157, GHSA-g7xg-7c54-rmpj

## What is CVE-2021-41157?

CVE-2021-41157 is a medium-severity missing authorization vulnerability in signalwire freeswitch, published on 26 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

FreeSWITCH is a Software Defined Telecom Stack enabling the digital transformation from proprietary telecom switches to a software implementation that runs on any commodity hardware. By default, SIP requests of the type SUBSCRIBE are not authenticated in the affected versions of FreeSWITCH. Abuse of this security issue allows attackers to subscribe to user agent event notifications without the need to authenticate. This abuse poses privacy concerns and might lead to social engineering or similar attacks. For example, attackers may be able to monitor the status of target SIP extensions. Although this issue was fixed in version v1.10.6, installations upgraded to the fixed version of FreeSWITCH from an older version, may still be vulnerable if the configuration is not updated accordingly. Software upgrades do not update the configuration by default. SIP SUBSCRIBE messages should be authenticated by default so that FreeSWITCH administrators do not need to explicitly set the `auth-subscriptions` parameter. When following such a recommendation, a new parameter can be introduced to explicitly disable authentication.

Weakness: CWE-306 (Missing Authentication for Critical Functionality), CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2021-41157?

It affects 1 product.


Products: Freeswitch Freeswitch.

## How do I fix CVE-2021-41157?

Change a configuration setting.

## Is CVE-2021-41157 being exploited?

There is no known exploitation of CVE-2021-41157 in the wild and no public exploit code.

## Other vulnerabilities in signalwire freeswitch

- [CVE-2026-49841](https://insights.sbomify.com/CVE-2026-49841/): FreeSWITCH: Pre-authentication heap buffer overflow in `mod_verto` HTTP POST body read (critical 9.8)
- [CVE-2019-19492](https://insights.sbomify.com/CVE-2019-19492/): Hardcoded credentials in n/a (critical 9.8)
- [CVE-2026-49840](https://insights.sbomify.com/CVE-2026-49840/): FreeSWITCH: Pre-authentication heap buffer overflow in libesl `Content-Length` parsing (critical 9.1)
- [CVE-2021-41145](https://insights.sbomify.com/CVE-2021-41145/): FreeSWITCH susceptible to Denial of Service via SIP flooding (high 8.6)
- [CVE-2026-45771](https://insights.sbomify.com/CVE-2026-45771/): Freeswitch Denial-of-Service in SIP PUBLISH Requests via XML Entity Expansion (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-41157 and fix it if it is affected.

What it is: CVE-2021-41157 is a medium-severity missing authorization vulnerability in signalwire freeswitch, published on 26 Oct 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-2021-41157 in the wild and no public exploit code.

Affected product: signalwire freeswitch. 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-2021-41157/ (Markdown: https://insights.sbomify.com/CVE-2021-41157/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-41157
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-41157
- OSV: https://osv.dev/vulnerability/CVE-2021-41157

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-41157/
Summaries are generated and may contain mistakes; the official description above is the record.