CVE-2026-49840Network attack vector

Pre-authentication heap corruption via negative Content-Length

Published Jun 9, 2026 · Updated Jun 9, 2026

Heap buffer overflow in FreeSWITCH before 1.11.1 allows remote attackers to corrupt or crash libesl clients via a crafted ESL frame. The esl_recv_event() function parses a negative Content-Length with atol(), allocates len + 1 bytes without sign or magnitude checks, and copies peer-controlled data outside the allocation. Remote attackers must control or intercept an ESL peer on the trusted control-plane segment; no credentials or prior interaction are required, and remote code execution has not been demonstrated.

CVSS severity9.1
Critical
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap buffer overflow in FreeSWITCH before 1.11.1 allows remote attackers to corrupt or crash libesl clients via a crafted ESL frame. The esl_recv_event() function parses a negative Content-Length with atol(), allocates len + 1 bytes without sign or magnitude checks, and copies peer-controlled data outside the allocation. Remote attackers must control or intercept an ESL peer on the trusted control-plane segment; no credentials or prior interaction are required, and remote code execution has not been demonstrated.

The record

CVE
CVE-2026-49840
Published
Jun 9, 2026
Updated
Jun 9, 2026
Vendor
SignalWire
Product
FreeSWITCH
Classifications
CWE-20, CWE-195, CWE-122, CWE-787, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.11.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

SignalWire · FreeSWITCHversion=< 1.11.1

Published CVSS scores

9.1GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
CWE-195Signed to Unsigned Conversion Error
CWE-122Heap-based Buffer Overflow
CWE-787Out-of-bounds Write
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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