CVE-2021-45487Network attack vector

Network activity disclosure via sequential IPv4 identifiers

Published Dec 25, 2021 · Updated Aug 4, 2024

Information disclosure in NetBSD through 9.2 allows remote attackers to infer kernel network activity from predictable IPv4 IDs. The kernel leaves IPv4 ID randomization disabled by default and uses a simple counter for packets longer than 68 bytes, exposing changes in shared protocol state. An attacker must elicit and observe IPv4 responses; sampled counter changes support host aliasing, de-NATing, idle scanning, or covert data exfiltration across firewalls.

CVSS severity7.5
High
EPSS probability0.96%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in NetBSD through 9.2 allows remote attackers to infer kernel network activity from predictable IPv4 IDs. The kernel leaves IPv4 ID randomization disabled by default and uses a simple counter for packets longer than 68 bytes, exposing changes in shared protocol state. An attacker must elicit and observe IPv4 responses; sampled counter changes support host aliasing, de-NATing, idle scanning, or covert data exfiltration across firewalls.

The record

CVE
CVE-2021-45487
Published
Dec 25, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-330, CAPEC-485, CAPEC-112, CAPEC-59
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 25, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/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 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-330Use of Insufficiently Random Values
CAPEC-485Signature Spoofing by Key Recreation
CAPEC-112Brute Force
CAPEC-59Session Credential Falsification through Prediction

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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