CVE-2026-116783 · Runtime
NO FIX YET · SEE WHAT TO DO
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.
first public Oct 28, 2026 · 1 source
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Deployments running FreeSWITCH with the mod_spandsp T.38 fax path reachable by peers that can send UDPTL to an established fax session, including fax applications and T.38 gateways. Systems without T.38 fax enabled or not reachable by untrusted peers are less exposed. The sources do not describe exposure beyond this.
Not affected if no-untrusted-peers, t38-disabled
Who cares freeswitch, self-hosted, telephony
fs_cli -x version or freeswitch -versionmod_spandsp is loaded and T.38 fax is enabled in your gateways or fax applications1.11.2 or laterFreeSWITCH 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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