FreeBSD-SA-08:05.openssh - OpenSSH X11-forwarding privilege escalation
久々の SA、今回は OpenSSH ですね。
I. Background OpenSSH is an implementation of the SSH protocol suite, providing an encrypted and authenticated transport for a variety of services, including remote shell access. The OpenSSH server daemon (sshd) provides support for the X11 protocol by binding to a port on the server and forwarding any connections which are made to that port. II. Problem Description When logging in via SSH with X11-forwarding enabled, sshd(8) fails to correctly handle the case where it fails to bind to an IPv4 port but successfully binds to an IPv6 port. In this case, applications which use X11 will connect to the IPv4 port, even though it had not been bound by sshd(8) and is therefore not being securely forwarded. III. Impact A malicious user could listen for X11 connections on a unused IPv4 port, e.g tcp port 6010. When an unaware user logs in and sets up X11 fowarding the malicious user can capture all X11 data send over the port, potentially disclosing sensitive information or allowing the execution of commands with the privileges of the user using the X11 forwarding. NOTE WELL: FreeBSD ships with IPv6 enabled by default in the GENERIC and SMP kernels, so users are vulnerable even they have not explicitly enabled IPv6 networking. IV. Workaround Disable support for IPv6 in the sshd(8) daemon by setting the option "AddressFamily inet" in /etc/ssh/sshd_config. Disable support for X11 forwarding in the sshd(8) daemon by setting the option "X11Forwarding no" in /etc/ssh/sshd_config.
ということで
- IPv6 を disabled する
- X11Forwarding no にする
のいずれか、自分の環境で問題の無い方を実施するのが回避策、ということで合ってます?