oss-sec mailing list archives
Re: Re: hwclock(8) SUID privilege escalation
From: Tavis Ormandy <taviso () google com>
Date: Tue, 26 May 2015 12:53:04 -0700
On Tue, May 26, 2015 at 6:59 AM, Stephane Chazelas <stephane.chazelas () gmail com> wrote:
2015-05-26 12:47:47 +0200, up201407890 () alunos dcc fc up pt: [...]Please note that this is possible on Debian-derived (and therefore Ubuntu), because /bin/sh is provided by dash which does NOT make use of privmode (does not drop privileges if ruid != euid, unlike bash), which is a very stupid idea. privmode is surprisingly effective at mitigating some common vulnerability classes and misconfigurations, and it has been around since mid 90's. Indeed, Chet Ramey (bash author and maintainer) explains that the purpose of this is to prevent "bogus system(3)/popen(3) calls in setuid executables"[...] No, bash does NOT drop privileges if ruid != euid when called as sh either . If it were, it would break those commands that use system()/popen() from suid/sgid executables (which arguably they shouldn't be doing) and expect the euid/egid to be preserved.
Yes it does, you are most likely a Debian user. Debian patched bash to add the behavior you describe back because someone complained it broke uucp delivery in 1999 (see debian bug 52586). That is why popen() in setuid programs are usually only exploitable on Debian/Ubuntu, see this link for more discussion http://www.openwall.com/lists/oss-security/2013/08/22/12 Tavis.
Current thread:
- hwclock(8) SUID privilege escalation up201407890 (May 26)
- Re: hwclock(8) SUID privilege escalation Larry W. Cashdollar (May 26)
- Re: hwclock(8) SUID privilege escalation Stephane Chazelas (May 26)
- Re: Re: hwclock(8) SUID privilege escalation Tavis Ormandy (May 26)
- <Possible follow-ups>
- Re: Re: hwclock(8) SUID privilege escalation up201407890 (May 26)
- Re: Re: hwclock(8) SUID privilege escalation Stephane Chazelas (May 26)