Date: Wed, 11 Jul 2012 09:08:12 -0500 From: Dustin Kirkland <dustin.kirkland@...zang.com> To: Tyler Hicks <tyhicks@...onical.com> Cc: oss-security@...ts.openwall.com, Marcus Meissner <meissner@...e.de>, Kurt Seifried <kseifried@...hat.com>, Dan Rosenberg <dan.j.rosenberg@...il.com> Subject: Re: ecryptfs headsup On Tue, Jul 10, 2012 at 5:15 PM, Tyler Hicks <tyhicks@...onical.com> wrote: > On 2012-07-10 15:13:40, Tyler Hicks wrote: >> On 2012-07-10 16:48:26, Dan Rosenberg wrote: >> > 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. >> >> This vulnerability is limited to physical access via formatted USB >> drives because the eCryptfs filesystem code does not work on top of >> network filesystems. >> >> Additionally, I believe that the encrypted home source and destination >> mount points were hard-coded up until ecryptfs-utils version 86. >> Versions before that should not be vulnerable to the setuid-root binary >> on a USB drive attack mentioned above. >> >> Dustin - Would you have any objections to forcing the nosuid and nodev >> mount options in the mount.ecryptfs_private helper? Hi Tyler, et al.- I don't have any objections at all with adding nosuid and nodev to the hardcoded mount.ecryptfs_private options. Actually, I seem to recall this coming up recently before. I can't find the bug or email thread (must have been IRC), but I recall offering to commit, test, and release that change immediately. I believe I was asked to wait to do that until a CVE had been published... I can't find any record of that conversation though, so that's just from memory. Shall I go ahead and commit/test/release that now, Tyler? -- :-Dustin Dustin Kirkland Chief Architect Gazzang, Inc. www.gazzang.com
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