Date: Fri, 26 Sep 2014 14:12:43 -0400 From: Rich Felker <dalias@...c.org> To: oss-security@...ts.openwall.com Subject: Re: Re: CVE-2014-6271: remote code execution through bash (3rd vulnerability) On Fri, Sep 26, 2014 at 02:06:21PM +0100, Simon McVittie wrote: > > Tell everyone to stop using setuid/setgid now and forever? Yes! > Minimizing use of setuid/setgid, and making sure the setuid/setgid > things are suitably hardened, is a good idea. However, tools for > controlled privilege escalation (sudo, pkexec, Apache suexec) rely on > setuid in order to work. There's a reason the feature exists at all. These could all be done by having the process with root privileges inherit them from a daemon parent that already has root, rather than requiring the kernel to elevate the privileges of a process via the setuid bit. This inherently eliminates all attacker control of the process's initial state and limits the input/attack surface to the communication channel clients have with the daemon (e.g. a single unix socket). As a bonus, a kernel that completely lacks setuid/setgid support immediately allows you to do lots of other security/functionality enhancements, like allowing any process to chroot at any time, allowing bind-mount-like filters blocking/replacing a process's view of part of the filesystem, etc. > I still think a large part of the answer is "consider it to be a serious > bug when a setuid/setgid tool does non-trivial things without first > filtering its attacker-controlled environment through a whitelist". The problem with this is that the environmental state (I don't mean just env vars, but everything a process inherits) is not of fixed scope, but continually growing, and each new feature added is a potential channel through which an attacker controls the behavior of the setuid process. Rich
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