Vulnerability · Published Jun 9, 2026 · Assigned by GitHub_M

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

Critical 9.1

In plain English

A critical-severity improper input validation in freeswitch from signalwire. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 24% of all known vulnerabilities).

Severity (CVSS 3.1)9.1Critical

Exploit odds (30 days)0.3%top 76.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 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.

Affected products (as reported)

Vendor	Product	Versions
signalwire	freeswitch	< 1.11.1

Weakness: CWE-20, CWE-122, CWE-195, CWE-787 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

References

https://github.com/signalwire/freeswitch/security/advisories/GHSA-g597-9fgg-ghg9 x_refsource_CONFIRM
https://github.com/signalwire/freeswitch/releases/tag/v1.11.1 x_refsource_MISC