CVE-2026-116783: FreeSWITCH mod_spandsp: out-of-bounds write parsing UDPTL error-recovery data

Vulnerability summary

CVE-2026-116783 is a high (CVSS 8.2) Improper Validation of Array Index vulnerability in signalwire freeswitch. EPSS estimates a 0.62% chance of exploitation in the next 30 days, higher than 49.9% of scored vulnerabilities.

Timeline

1. 05-11-2026
   PublishedVulnerability first disclosed.
2. 09-11-2026
   Last modifiedVulnerability information updated.

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. 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.

• CWE-129Improper Validation of Array IndexThe product uses untrusted input when calculating or using an array index, but the product does not validate or incorrectly validates the index to ensure the index references a valid position within the array.
• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.