CVE-2021-3384Network attack vector

Temporary network isolation via NDP timeout mishandling

Published Mar 2, 2021 · Updated Aug 3, 2024

Denial of service in affected Stormshield Network Security releases allows remote attackers to block contact with new IPv4 or IPv6 hosts. The IPv6 Neighbor Discovery timeout handler permits crafted network traffic to trigger ARP/NDP table protection instead of maintaining entries for new destinations. Exploitation requires network reachability but no authentication or user interaction, and the resulting service interruption is temporary rather than a device crash or reboot.

CVSS severity5.3
Medium
EPSS probability1.02%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in affected Stormshield Network Security releases allows remote attackers to block contact with new IPv4 or IPv6 hosts. The IPv6 Neighbor Discovery timeout handler permits crafted network traffic to trigger ARP/NDP table protection instead of maintaining entries for new destinations. Exploitation requires network reachability but no authentication or user interaction, and the resulting service interruption is temporary rather than a device crash or reboot.

The record

CVE
CVE-2021-3384
Published
Mar 2, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1498
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 2, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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?

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

4.4StormshieldCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:U/RL:O/RC:R
5.3StormshieldCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
5.3NIST NVDCVSS: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 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

T1498Network Denial of Service

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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