Vulnerability Intelligence Report
FreeSWITCH: Pre-authentication heap buffer overflow in libesl `Content-Length` parsing
CVE-2026-49840
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.
No Active Exploit Signals
CVSS Base Score
9.1
CRITICAL
Exploitability:3.9
Impact Score:5.2
EPSS Probability:0.31%
Executive Threat Verdict
Evaluating...
Evaluating Threat Landscape...
Assessing known weaponization, exploitation telemetry, and federal advisories.
Attack Surface
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Authentication
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Weaponization
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SSVC Action
—
Weaknesses (CWE)
Affected Products & Versions
| Vendor | Product | Affected Versions |
|---|---|---|
| signalwire | freeswitch | < 1.11.1 (affected) |
Threat Intelligence Signals
EPSS Score
0.310%
Identity & Timeline
| Status | PUBLISHED |
| Assigning Authority | GitHub, Inc. · Vendor · USA |
| Reserved | 2026-06-01T18:50:36 |
| Published | 2026-06-09T16:00:56 |
| Last Updated | 2026-06-09T17:00:21 |
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