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CVE-2026-49840

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

Published: Jun 9, 2026Updated: Jun 10, 2026 Sources: CVE List NVDCWE-20
NVD MITRE
9.1CVSSCRITICAL
EPSS Score
0.3%
Top 82.0%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
No Fix Available

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.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:HIntegrity
High
A:HAvailability
High
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Weaknesses

CWE-20CWE-122CWE-195CWE-787

Affected Products

freeswitchsignalwire
Mixed
Communications / voip-telephony
freeswitchfreeswitch
On-prem
Communications / voip-telephony
signalwirecommercialCommunicationsaka freeswitch (related), sofia-sip (related)
freeswitchoss-projectCommunications

Attack Graph

Products CVE Techniques Tactics

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Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

MITRE ATT&CK

2 techniques
Initial Access
Privilege Escalation
View detailed technique mapping

References

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

Timeline

Published
Jun 9, 2026
Last Updated
Jun 10, 2026
News mentions
1

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