CVE-2020-11091 Information

Description

In Weave Net before version 2.6.3 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. Weave Net version 2.6.3 disables the accept_ra option on the veth devices that it creates.

CVSS Vector

CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:N/I:H/A:N

Reference

https://github.com/weaveworks/weave/commit/15f21f1899060f7716c70a8555a084e836f39a60 https://github.com/weaveworks/weave/security/advisories/GHSA-59qg-grp7-5r73

Attack Complexity

HIGH

Privileges Required

HIGH

User Interaction Required

HIGH

Scope

NONE

Confidentiality Impact

CHANGED

Integrity Impact

NONE

Availability Impact

HIGH

Base Score

NONE

Base Severity

5.8