---
id: "CVE-2026-116567"
kind: "vulnerability"
aliases: ["CVE-2026-116567"]
title: "FreeSWITCH: unauthenticated RTMP message overflows stack, crashes telephony server"
severity: "high"
cvss: 7.5
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["freeswitch", "runtime", "telephony", "voip"]
not_affected_if: ["default-config", "mod-rtmp-not-loaded", "port-1935-filtered"]
published_at: "2026-11-05T20:17:43+00:00"
first_seen_at: "2026-11-05T20:40:44+00:00"
updated_at: "2026-11-05T20:43:09+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-116567", "first_seen_at": "2026-11-05T20:40:44+00:00"}]
exploit_sources: []
---

# FreeSWITCH: unauthenticated RTMP message overflows stack, crashes telephony server

FreeSWITCH before 1.11.2 copies an RTMP user-control message into a fixed 200-byte stack buffer without a length limit, so a body of about 70 bytes or more overflows the stack. An attacker who can reach the RTMP listener without logging in can crash FreeSWITCH and drop every active call.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the FreeSWITCH version with `fs_cli -x version` or `freeswitch -version`; anything below `1.11.2` is affected.
- Check whether mod_rtmp is loaded with `fs_cli -x "module_exists mod_rtmp"` or by looking for mod_rtmp in the modules.conf file.
- If mod_rtmp is loaded, check whether TCP port 1935 is listening and reachable from outside the host.

## Fix

- Upgrade FreeSWITCH to `1.11.2` or later.

## Timeline

- 2026-11-05T20:40:44+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-116567

## Documents

- [advisory] Vendor advisory: github.com https://github.com/signalwire/freeswitch/security/advisories/GHSA-hj6x-9653-p796
- [fix] Patch: github.com https://github.com/signalwire/freeswitch/commit/fc0db829b87d1a5a3043e355b4294c41851b13c6
- [fix] Release notes: github.com https://github.com/signalwire/freeswitch/releases/tag/v1.11.2

## From the sources

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. Prior to 1.11.2, rtmp_handle_control() rendered an RTMP user-control message into a 200-byte stack buffer using an unbounded sprintf loop controlled by the wire message length. A body of roughly 70 bytes or more overflowed the stack before any RTMP login, because the handshake authenticates neither side. The flaw affects deployments that build and load mod_rtmp, which is disabled in the stock build and configuration but commonly exposes a listener on TCP port 1935 when enabled. One unauthenticated message can crash FreeSWITCH and end every active call; the constrained ASCII hex output has not yielded control-flow hijacking. This issue is fixed in version 1.11.2.

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