CVE-2026-49840
FreeSWITCH: Pre-authentication heap buffer overflow in libesl `Content-Length` parsing
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.
INFO
Published Date :
June 9, 2026, 5:17 p.m.
Last Modified :
June 10, 2026, 3:06 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-49840
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | CRITICAL | [email protected] |
Solution
- Update FreeSWITCH to version 1.11.1 or later.
- Apply the patch for esl_recv_event() handling.
- Ensure all linked processes are updated.
- Validate heap integrity after update.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-49840.
| URL | Resource |
|---|---|
| https://github.com/signalwire/freeswitch/releases/tag/v1.11.1 | Release Notes |
| https://github.com/signalwire/freeswitch/security/advisories/GHSA-g597-9fgg-ghg9 | Third Party Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-49840 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-49840
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-49840 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-49840 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Jun. 10, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:freeswitch:freeswitch:*:*:*:*:*:*:*:* versions up to (excluding) 1.11.1 Added Reference Type GitHub, Inc.: https://github.com/signalwire/freeswitch/releases/tag/v1.11.1 Types: Release Notes Added Reference Type GitHub, Inc.: https://github.com/signalwire/freeswitch/security/advisories/GHSA-g597-9fgg-ghg9 Types: Third Party Advisory -
New CVE Received by [email protected]
Jun. 09, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H Added CWE CWE-20 Added CWE CWE-787 Added CWE CWE-122 Added CWE CWE-195 Added Reference https://github.com/signalwire/freeswitch/releases/tag/v1.11.1 Added Reference https://github.com/signalwire/freeswitch/security/advisories/GHSA-g597-9fgg-ghg9