CVE-2026-116781: FreeSWITCH: Pre-authentication out-of-bounds writes in mod_xml_rpc WebSocket frame parsing

Vulnerability summary

CVE-2026-116781 is a medium (CVSS 5.3) Off-by-one Error vulnerability in signalwire freeswitch. EPSS estimates a 0.27% chance of exploitation in the next 30 days, higher than 18.5% 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, ws_read_frame() unmasked a WebSocket payload by iterating wsh->datalen, which included frame headers, while indexing from the payload pointer. A masked frame filling the 64 KiB receive buffer could therefore XOR up to 14 bytes beyond the buffer, and the exact-capacity case also wrote a terminating NUL one byte out of bounds. The flaw is reachable before authentication when mod_xml_rpc and its opt-in WebSocket endpoint are enabled, while both features are disabled in the stock configuration. The writes remain within the same connection handle's adjacent outbound buffer, so neither a process crash nor cross-session disclosure has been demonstrated. This issue is fixed in version 1.11.2.

• CWE-193Off-by-one ErrorA product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.
• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.