How severe is CVE-2020-11091?

CVE-2020-11091 has a CVSS score of 5.8/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2020-11091?

CVE-2020-11091 affects the following packages: github.com/weaveworks/weave (Go). Ecosystems affected: Go.

How do I fix CVE-2020-11091?

Update github.com/weaveworks/weave to 2.6.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-11091 is resolved across your whole dependency graph.

How do I detect CVE-2020-11091 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/weaveworks/weave, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2020-11091 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2020-11091 actively exploited in the wild?

No public exploit code has been indexed for CVE-2020-11091 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2020-11091?

CVE-2020-11091 has an EPSS (Exploit Prediction Scoring System) score of 0.9%, placing it in the 57th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2020-11091?

CVE-2020-11091 is classified as CWE-350 (CWE-350). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2020-11091 published, and has it been updated?

CVE-2020-11091 was published on June 3, 2020 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

MEDIUM severity

CVE-2020-11091 — weave

MEDIUMFix: weaveworks/weave@15f21f1

CVE-2020-11091 is a medium-severity (CVSS 5.8) CWE-350 vulnerability in github.com/weaveworks/weave. A fix is available for github.com/weaveworks/weave — see the affected versions and patch details below.

Weave Net clusters susceptible to MitM attacks via IPv6 rogue router advertisements

Also known asGHSA-59qg-grp7-5r73GO-2022-0794

Published

Jun 3, 2020

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.9%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs57th percentile — riskier than 57% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2020-11091 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐹github.com/weaveworks/weave

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

An attacker able to run a process as root in a container is able to respond to DNS requests from the host and thereby insert themselves as a fake service.

In a cluster with an IPv4 internal network, if IPv6 is not totally disabled on the host (via ipv6.disable=1 on the kernel cmdline), it will be either unconfigured or configured on some interfaces, but it’s pretty likely that ipv6 forwarding is disabled, ie /proc/sys/net/ipv6/conf//forwarding == 0. Also by default, /proc/sys/net/ipv6/conf//accept_ra == 1. The combination of these 2 sysctls means that the host accepts router advertisements and configure the IPv6 stack using them.

By sending “rogue” router advertisements, an attacker can reconfigure the host to redirect part or all of the IPv6 traffic of the host to the attacker controlled container. Even if there was no IPv6 traffic before, if the DNS returns A (IPv4) and AAAA (IPv6) records, many HTTP libraries will try to connect via IPv6 first then fallback to IPv4, giving an opportunity to the attacker to respond. If by chance you also have on the host a vulnerability like last year’s RCE in apt (CVE-2019-3462), you can now escalate to the host.

Patches

Weave Net version 2.6.3 (to be released soon) will disable the accept_ra option on the veth devices that it creates.

Workarounds

Users should not run containers with CAP_NET_RAW capability. This has been the advice from Weave Net for years. https://www.weave.works/docs/net/latest/kubernetes/kube-addon/#-securing-the-setup

For more information

If you have any questions or comments about this advisory:

Open an issue in the Weave Net repo
Join the <a href="https://slack.weave.works/" target="_blank">Weave Users Slack</a>.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/weaveworks/weave`	all versions	2.6.3`go get github.com/weaveworks/weave@v2.6.3`

Affected Products

1 product · 1 configurations

Application

weave netweave

< 2.6.3

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/weaveworks/weave, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/weaveworks/weave to 2.6.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-11091 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Impact An attacker able to run a process as root in a container is able to respond to DNS requests from the host and thereby insert themselves as a fake service. In a cluster with an IPv4 internal network, if IPv6 is not totally disabled on the host (via ipv6.disable=1 on the kernel cmdline), it will be either unconfigured or configured on some interfaces, but it’s pretty likely that ipv6 forwarding is disabled, ie /proc/sys/net/ipv6/conf//forwarding == 0. Also by default, /proc/sys/net/ipv6/conf//accept_ra == 1. The combination of these 2 sysctls means that the host accepts router advert