CVE-2026-49840 CRITICAL

CVE-2026-49840: FreeSWITCH: Pre-authentication heap buffer overflow in libesl `Content-Length` parsing

Vendor Signalwire
Product freeswitch
Weakness CWE-20 · Input validation
Published June 9, 2026
Last update June 9, 2026
View on NVD All CVEs

CVSS base score

9.1/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality None
Integrity High

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

June 9, 2026 CVE published
June 9, 2026 Record updated