CVE-2026-5661Public exploitNetwork attack vector

Service disruption via contradictory NGSetup responses

Published Apr 6, 2026 · Updated Apr 6, 2026

Improper request handling in free5GC 4.2.0 allows remote attackers to disrupt NGAP client state via a crafted NGSetupRequest. The AMF handler sends NGSetupFailure for an unrecognized IE with notify criticality, then continues and sends NGSetupResponse instead of returning. SCTP access to the AMF NGAP interface is sufficient; the contradictory replies can desynchronize the requesting client.

CVSS severity5.3
Medium
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper request handling in free5GC 4.2.0 allows remote attackers to disrupt NGAP client state via a crafted NGSetupRequest. The AMF handler sends NGSetupFailure for an unrecognized IE with notify criticality, then continues and sends NGSetupResponse instead of returning. SCTP access to the AMF NGAP interface is sufficient; the contradictory replies can desynchronize the requesting client.

The record

CVE
CVE-2026-5661
Published
Apr 6, 2026
Updated
Apr 6, 2026
Vendor
free5GC
Product
free5GC
Classifications
CWE-404, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 6, 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=4.2.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

free5GC · free5GCversion=4.2.0

Published CVSS scores

5.5VulDBCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
5.0VulDBAV:N/AC:L/Au:N/C:N/I:N/A:P
5.3VulDBCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitPublished

Weakness, pattern, technique

CWE-404Improper Resource Shutdown or Release
T1499.004Application or System Exploitation

Public exploit references

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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