CVE-2026-40249Network attack vector

Unintended subscription updates via fail-open PUT handling

Published Apr 16, 2026 · Updated Apr 16, 2026

Fail-open request handling in free5GC 4.2.1 and earlier allows remote attackers to attempt unintended subscription updates via malformed input. The UDR PUT handler calls its processor after body-read or deserialization errors and passes the subscription object directly instead of a pointer. Reachability requires network access to the SBI; successful data modification has not been demonstrated and depends on downstream processing and storage validation.

CVSS severity6.9
Medium
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Fail-open request handling in free5GC 4.2.1 and earlier allows remote attackers to attempt unintended subscription updates via malformed input. The UDR PUT handler calls its processor after body-read or deserialization errors and passes the subscription object directly instead of a pointer. Reachability requires network access to the SBI; successful data modification has not been demonstrated and depends on downstream processing and storage validation.

The record

CVE
CVE-2026-40249
Published
Apr 16, 2026
Updated
Apr 16, 2026
Vendor
free5GC
Product
free5GC
Classifications
CWE-754, CWE-636, T1565.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 16, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 16, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=<= 4.2.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

free5GC · free5GCversion=<= 4.2.1

Published CVSS scores

6.9GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions
CWE-636Not Failing Securely ('Failing Open')
T1565.001Stored Data Manipulation

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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