---
id: "CVE-2026-116783"
kind: "vulnerability"
aliases: ["CVE-2026-116783"]
title: "FreeSWITCH: crafted T.38 fax packets corrupt memory and crash calls"
severity: "high"
cvss: 8.2
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["freeswitch", "runtime", "self-hosted", "telephony"]
not_affected_if: ["no-untrusted-peers", "t38-disabled"]
published_at: "2026-11-05T20:17:45+00:00"
first_seen_at: "2026-11-05T20:40:45+00:00"
updated_at: "2026-11-05T20:42:55+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-116783", "first_seen_at": "2026-11-05T20:40:45+00:00"}]
exploit_sources: []
---

# FreeSWITCH: crafted T.38 fax packets corrupt memory and crash calls

FreeSWITCH, a software telephony switch, has a memory corruption bug in its T.38 fax handling (mod_spandsp) that a peer can trigger by sending crafted UDPTL packets. The corruption can crash FreeSWITCH and drop every active call, though remote code execution has not been demonstrated.

_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`
- Check whether `mod_spandsp` is loaded and T.38 fax is enabled in your gateways or fax applications
- Check whether the server accepts UDPTL/T.38 traffic from untrusted peers

## Fix

- FreeSWITCH: move to `1.11.2` or later

## Timeline

- 2026-11-05T20:40:45+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-116783

## Documents

- [advisory] Vendor advisory: github.com https://github.com/signalwire/freeswitch/security/advisories/GHSA-mjp3-3cq2-hxj4
- [fix] Patch: github.com https://github.com/signalwire/freeswitch/commit/b999d2a594f025ac0dd4d7b137635308ef298272
- [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, udptl_rx_packet() used a peer-controlled FEC entry count directly to fill five-entry FEC arrays in a mod_spandsp T.38 session. A larger count wrote sender-controlled error-recovery data beyond those arrays and persisted the oversized count for a later reconstruction pass. Any peer able to deliver UDPTL to an established T.38 fax session can reach the parser, including deployments using fax applications or a T.38 gateway. The memory corruption can crash FreeSWITCH and end every active call, although remote code execution has not been demonstrated. This issue is fixed in version 1.11.2.

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