Date: Tue, 10 Jul 2012 16:48:26 -0400 From: Dan Rosenberg <dan.j.rosenberg@...il.com> To: oss-security@...ts.openwall.com CC: Marcus Meissner <meissner@...e.de>, Kurt Seifried <kseifried@...hat.com> Subject: Re: ecryptfs headsup On 07/10/2012 10:30 AM, Marcus Meissner wrote: > On Tue, Jul 10, 2012 at 04:21:13PM +0200, Sebastian Krahmer wrote: >> >> It is a potential privilege escalation since the pam module >> was not setting uid/gid(list) appropriately and the suid >> binary did not clear environment before exec'ing umount. >> I do not know whether MS_NOSUID was really needed (and maybe >> MS_NODEV is, but I was not able to create dev files). >> Unfortunally we found ecryptfs not really stable inside the kernel >> and Marcus is still rebooting :) > > This means ... > > So far we have not yet found a specific security issue. > > Ciao, Marcus > This reminds me... If an unprivileged user can mount ecryptfs shares (e.g. via the setuid-root mount helper shipped on Ubuntu) and has the ability to mount user-controlled filesystems (either network filesystems via setuid mount helpers like mount.cifs or mount.nfs, or formatted USB drives via physical access), it's possible to escalate privileges to root because the setuid ecryptfs helper does not mount filesystems with the nosuid or nodev flags. An attacker can create an ecryptfs filesystem on his own machine on a network filesystem or USB drive, and then mount that ecryptfs filesystem on the victim machine for a setuid-root backdoor. Hard-coding nosuid and nodev into the setuid ecryptfs helper would resolve this, but I'm not sure that's workable for Ubuntu home directories. -Dan
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