CVE-2021-20322Network attack vector

UDP port disclosure via predictable exception-cache eviction

Published Feb 18, 2022 · Updated Jul 30, 2026

ICMP error processing in Linux Kernel allows remote attackers to rapidly infer open UDP ports through off-path network probes. The IPv4 and IPv6 route exception caches use predictable collision limits and oldest-entry eviction, so forged ICMP errors reveal whether a UDP socket exists through cache state. Exploitation requires off-path ICMP probing; the resulting port oracle facilitates attacks against UDP services that depend on source-port randomization.

CVSS severity7.4
High
EPSS probability6.85%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

ICMP error processing in Linux Kernel allows remote attackers to rapidly infer open UDP ports through off-path network probes. The IPv4 and IPv6 route exception caches use predictable collision limits and oldest-entry eviction, so forged ICMP errors reveal whether a UDP socket exists through cache state. Exploitation requires off-path ICMP probing; the resulting port oracle facilitates attacks against UDP services that depend on source-port randomization.

The record

CVE
CVE-2021-20322
Published
Feb 18, 2022
Updated
Jul 30, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-330, T1046
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 18, 2022CVE publishedPublication date reported by the CVE source.
  2. Jul 30, 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=4.15 <4.19.215
  2. Affected versionversion=4.20 <5.4.146
  3. Affected versionversion=5.11 <5.13.17
  4. Affected versionversion=5.14 <5.14.4
  5. Affected versionversion=5.5 <5.10.65

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=4.15 <4.19.215; version=4.20 <5.4.146; version=5.11 <5.13.17; version=5.14 <5.14.4; version=5.5 <5.10.65

Published CVSS scores

7.4Ubuntu Security TeamCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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
T1046Network Service Discovery

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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