# CVE-2026-116783: FreeSWITCH buffer overflow in mod_spandsp UDPTL FEC parsing

Source: https://junglewise.ai/threats/cve-2026-116783-freeswitch-is-a-software-defined-telecom-stack-enabling-the  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-05. Updated: 2026-11-05  
License: CC BY 4.0 with a link back

CVE-2026-116783 · Severity: high · CVSS 8.2 · Published 2026-11-05

FreeSWITCH is a software-based telephone exchange that replaces proprietary hardware switches. The mod_spandsp module handles T.38 fax sessions over IP, and a buffer overflow in its UDPTL packet parser allows remote attackers to crash the system and terminate all active calls. An attacker only needs the ability to send fax packets to an established session, a threat to both direct fax deployments and T.38 gateways.

Technologies: [SignalWire FreeSWITCH](https://junglewise.ai/threats/technologies/freeswitch). Vendors: [SignalWire](https://junglewise.ai/threats/vendors/signalwire).

## Quick answers

**Is CVE-2026-116783 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-116783 being exploited in the wild.

**How severe is CVE-2026-116783?** High severity, with a CVSS score of 8.2, published 5 November 2026.

**Which products and versions are affected?** SignalWire FreeSWITCH prior to 1.11.2.

**Is there a fix for CVE-2026-116783?** Yes: fixed in 1.11.2. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-116783 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-116783?** Check whether you run SignalWire FreeSWITCH at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 1.11.2

## Technical details

The udptl_rx_packet() function in mod_spandsp accepts a peer-controlled FEC (forward error correction) entry count from UDPTL packets without validating it against the fixed-size fec[] and fec_len[] arrays, which hold only LOCAL_FAX_MAX_FEC_PACKETS entries. Additionally, secondary redundancy element lengths are copied into a fixed-size buffer without bounds checking. An attacker with network access to a T.38 session can craft packets with oversized counts or lengths to trigger out-of-bounds writes and memory corruption.

## Affected products

- SignalWire FreeSWITCH prior to 1.11.2

## Timeline

- 2026-11-05: disclosed
- 2026-08-09: patched: v1.11.2 released

## References

- [https://github.com/signalwire/freeswitch/commit/b999d2a594f025ac0dd4d7b137635308ef298272](https://github.com/signalwire/freeswitch/commit/b999d2a594f025ac0dd4d7b137635308ef298272)
- [https://github.com/signalwire/freeswitch/releases/tag/v1.11.2](https://github.com/signalwire/freeswitch/releases/tag/v1.11.2)

## Related threats

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