CVE-2021-22161
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIn OpenWrt 19.07.x before 19.07.7, when IPv6 is used, a routing loop can occur that generates excessive network traffic between an affected device and its upstream ISP's router. This occurs when a link prefix route points to a point-to-point link, a destination IPv6 address belongs to the prefix and is not a local IPv6 address, and a router advertisement is received with at least one global unique IPv6 prefix for which the on-link flag is set. This affects the netifd and odhcp6c packages.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceOpenWrt versions 19.07.x before 19.07.7 contain a routing loop vulnerability in the netifd and odhcp6c packages. When IPv6 is enabled and a router advertisement is received with a global unique IPv6 prefix that has the on-link flag set, a routing loop can form between the affected device and upstream ISP router when certain prefix conditions are met, generating excessive network traffic.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 19.07.0, <= 19.07.6CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Adjacent
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify OpenWrt versionRun 'cat /etc/openwrt_version' or check via LuCI under System > Software, or use 'opkg list-installed' to find the base versionAffected if Version is 19.07.0, 19.07.1, 19.07.2, 19.07.3, 19.07.4, 19.07.5, or 19.07.6 (versions before 19.07.7)
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Confirm IPv6 is enabledInspect /etc/config/network for IPv6 settings on WAN interface, or run 'ip -6 addr show' to see if IPv6 addresses are assigned to WANAffected if IPv6 is enabled and the router is receiving router advertisements on the WAN interface
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Check netifd and odhcp6c packagesRun 'opkg list-installed | grep -E "^netifd |^odhcp6c "' to verify these packages are installedAffected if These packages are installed and handle IPv6 prefix processing for router advertisements
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Verify on-link IPv6 prefix handlingMonitor network traffic on WAN interface for incoming Router Advertisement messages using 'tcpdump -i eth0 -vv ip6' or check logs for prefix-related messagesAffected if Router is processing router advertisements that contain global unique IPv6 prefixes with the on-link flag set
The router is affected if it runs OpenWrt 19.07.0 through 19.07.6 with IPv6 enabled and is receiving router advertisements containing global unique IPv6 prefixes with the on-link flag set from the upstream ISP.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpgrade OpenWrt to version 19.07.7 or later which contains the fix for this routing loop vulnerability in the netifd and odhcp6c packages.
- Consultation3.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-22161 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-22161 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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