CVE-2026-49840 — FreeSWITCH: Pre-authentication heap buffer overflow in libesl `Content-Length` parsing
FreeSWITCH is a Software Defined Telecom Stack enabling the digital transformation from proprietary telecom switches to a software implementation that runs on any commodity hard…
Published: 2026-06-09 · CVSS: 9.1 · CVSS 3.1
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 version 1.11.1, esl_recv_event() parses Content-Length with atol() and passes the result straight to malloc(len + 1) with no sign or magnitude check. A malicious or man-in-the-middle ESL peer can send a frame with a negative Content-Length to corrupt the heap of, or crash, any process linked against libesl, before the client has authenticated to that peer. This issue has been patched in version 1.11.1.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7