CVE-2021-22161

Denial of service via IPv6 routing loop

Published Feb 7, 2021 · Updated Aug 3, 2024

Denial of service in OpenWrt 19.07.0 through 19.07.6 allows adjacent attackers to generate excessive IPv6 traffic via crafted packets. The netifd and odhcp6c packages install an on-link prefix route on a point-to-point WAN, causing nonlocal traffic within that prefix to bounce between the device and its upstream router. Reachability requires IPv6, a point-to-point interface such as PPP, and a router advertisement carrying a global unique prefix with the on-link flag set; the documented consequence is sustained traffic amplification rather than data access or modification.

CVSS severity6.5
Medium
EPSS probability0.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in OpenWrt 19.07.0 through 19.07.6 allows adjacent attackers to generate excessive IPv6 traffic via crafted packets. The netifd and odhcp6c packages install an on-link prefix route on a point-to-point WAN, causing nonlocal traffic within that prefix to bounce between the device and its upstream router. Reachability requires IPv6, a point-to-point interface such as PPP, and a router advertisement carrying a global unique prefix with the on-link flag set; the documented consequence is sustained traffic amplification rather than data access or modification.

The record

CVE
CVE-2021-22161
Published
Feb 7, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-835, T1498
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 7, 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 vectoradjacent
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.3NIST NVDAV:A/AC:L/Au:N/C:N/I:N/A:P

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)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo