Date: Sun, 3 Aug 1997 10:21:09 -0500 From: Karl Denninger <karl@Mcs.Net> To: Marc Slemko <marcs@znep.com> Cc: freebsd-security@FreeBSD.ORG Subject: Re: Vulnerability in 4.4BSD rfork() implementation Message-ID: <19970803102109.40387@Jupiter.Mcs.Net> In-Reply-To: <Pine.BSF.3.95.970802214104.12645Y-100000@alive.znep.com>; from Marc Slemko on Sat, Aug 02, 1997 at 09:53:52PM -0600 References: <199708030102.UAA20008@enteract.com> <Pine.BSF.3.95.970802214104.12645Y-100000@alive.znep.com>
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The patch does not build on -CURRENT; the make process returns a complaint for the DISPATCH macro. The kernel patch *is* effective. -- -- Karl Denninger (karl@MCS.Net)| MCSNet - The Finest Internet Connectivity http://www.mcs.net/~karl | T1's from $600 monthly to FULL DS-3 Service | 99 Analog numbers, 77 ISDN, http://www.mcs.net/ Voice: [+1 312 803-MCS1 x219]| NOW Serving 56kbps DIGITAL on our analog lines! Fax: [+1 312 803-4929] | 2 FULL DS-3 Internet links; 400Mbps B/W Internal On Sat, Aug 02, 1997 at 09:53:52PM -0600, Marc Slemko wrote: > On Sat, 2 Aug 1997, Thomas H. Ptacek wrote: > > > ---------------------------------------------------------------------------- > > > > OpenBSD Security Advisory > > > > August 2, 1997 > > > > Vulnerability in rfork() System Call > > > > ---------------------------------------------------------------------------- > > > > SYNOPSIS > > > > A vulnerability in certain 4.4BSD kernels allows processes to gain > > access to restricted resources by manipulating the file descriptor > > tables of SUID and SGID executables. Applications of this vulnerability > > will allow users to gain root access. > > > > ---------------------------------------------------------------------------- > > > > AFFECTED SYSTEMS > > > > It is believed that all 4.4BSD operating systems implementing the > > rfork() system call are currently vulnerable to this problem. These > > operating systems include OpenBSD 2.1 and FreeBSD 3.0. The OpenBSD > > project has resolved this problem in OpenBSD-current. > > Since this wasn't entirely clear on some of the FreeBSD aspects, a few > comments... > > First, this is a real hole. Earlier today it took me only a few minutes > to make a program to add another uid 0 to your passwd file to give you > root access. With the skeleton code posted in this advisory, it is even > easier. > > Secondly, FreeBSD 2.2 (probably any version of 2.2-current starting > around 1996/02/23) and 3.0 are both vulnerable. 2.1 and earlier are not. > > Third, I would recommend the use of the loadable module included in the > advisory to close the hole temporarily until there is a FreeBSD advisory > or patch. While the supplied patch for kern_exec looks fine, using the > module is easier and saves you having to do things twice when an official > patch comes out. Few things (very few...) use rfork() so it shouldn't > hurt much. > > To use the loadable module, unarchive the shell archive included in the > origial post, type "make", then do something like: > > modload -e disable_rfork disable_rfork.o > > as root. You should get a kernel message that the rfork() call is > disabled. You should probably make it load at boot to prevent someone > from deliberately crashing the system to remove the protection. >
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