signalwire FreeSWITCH up to 1.11.0 esl_recv_event channel accessible

Summaryinfo

A vulnerability classified as critical has been found in signalwire FreeSWITCH up to 1.11.0. The impacted element is the function esl_recv_event. The manipulation leads to channel accessible. This vulnerability is listed as CVE-2026-49840. The attack may be initiated remotely. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, has been found in signalwire FreeSWITCH up to 1.11.0. This issue affects the function esl_recv_event. The manipulation with an unknown input leads to a channel accessible vulnerability. Using CWE to declare the problem leads to CWE-300. The product does not adequately verify the identity of actors at both ends of a communication channel, or does not adequately ensure the integrity of the channel, in a way that allows the channel to be accessed or influenced by an actor that is not an endpoint. Impacted is integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-49840 since 06/01/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1557 for this issue.

Upgrading to version 1.11.1 eliminates this vulnerability. The upgrade is hosted for download at github.com.

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Productinfo

Vendor

• signalwire

Name

• FreeSWITCH

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.9
• 1.10
• 1.11.0

Website

• Product: https://github.com/signalwire/freeswitch/

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