CVE-2021-45489Public exploitNetwork attack vector

Information disclosure via predictable IPv6 flow labels

Published Dec 25, 2021 · Updated Aug 4, 2024

Information disclosure in NetBSD through 9.2 allows remote attackers to infer kernel network state from TCP/IPv6 flow labels. The A2/20 generator holds its parameters between reseeds, allowing roughly 100 consecutive labels to reveal its state and predict later outputs. Exploitation requires a reachable TCP/IPv6 service and collection of consecutive labels; the recovered state supports host aliasing, idle scanning, or a low-bandwidth covert channel.

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 state from TCP/IPv6 flow labels. The A2/20 generator holds its parameters between reseeds, allowing roughly 100 consecutive labels to reveal its state and predict later outputs. Exploitation requires a reachable TCP/IPv6 service and collection of consecutive labels; the recovered state supports host aliasing, idle scanning, or a low-bandwidth covert channel.

The record

CVE
CVE-2021-45489
Published
Dec 25, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-338, T1048
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 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 exploitPublished

Weakness, pattern, technique

CWE-338Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)
T1048Exfiltration Over Alternative Protocol

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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