Bugzilla Bug 74477

Advisory from securesoftware@list.cr.yp.to:

Date: 15 Dec 2004 08:20:49 -0000
From: "D. J. Bernstein" <djb@cr.yp.to>
Subject: [remote] [control] NASM 0.98.38 error() overflows buff[]
To: securesoftware@list.cr.yp.to, nasm-devel@lists.sourceforge.net
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Jonathan Rockway, a student in my Fall 2004 UNIX Security Holes course,
has discovered a remotely exploitable security hole in NASM. I'm
publishing this notice, but all the discovery credits should be assigned
to Rockway.

You are at risk if you receive an asm file from an email message (or a
web page or any other source that could be controlled by an attacker)
and feed that file through NASM. Whoever provides that asm file then has
complete control over your account: he can read and modify your files,
watch the programs you're running, etc.

Of course, if you _run_ a program, you're authorizing the programmer to
take control of your account; but the NASM documentation does not say
that merely _assembling_ a program can have this effect. It's easy to
imagine situations in which a program is run inside a jail but assembled
outside the jail; this NASM bug means that the jail is ineffective.

Proof of concept: On an x86 computer running FreeBSD 4.10, as root, type

   cd /usr/ports/devel/nasm
   make install

to download and compile the NASM program, version 0.98.38 (current).
Then, as any user, save the file 22.S attached to this message, and type

   nasm 22.S

with the unauthorized result that a file named EXPLOITED is created in
the current directory. (I tested this with a 525-byte environment, as
reported by printenv | wc -c.)

Here's the bug: In preproc.c, error() uses an unprotected vsprintf() to
copy data into a 1024-byte buff[] array.

---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago

Created an attachment (id=46029) [details]
22.S from advisory

upstream is fixing :
http://sourceforge.net/mailarchive/forum.php?thread_id=6166881&forum_id=4978

Created an attachment (id=46130) [details]
nasm-0.98.38-overflow.patch

Patch to fix vsprintf vulnerabilities.

Mr Bones, please verify and apply patch.

It didn't "exploit" like it was described on the advisory but it did segfault. 
Applying the patch prevented the segfault.  Added to portage, rev bumped and
removed all previous versions of the ebuild.  glep at will.

The exploit is for a specific environment (FreeBSD 4.x, x86 etc.) and would
need to be adapted to the environment you're trying it on (Linux 2.6, etc.) to
do exactly what is described. The SegFault shows that you're most probably
vulnerable, though.  Thanks for releasing a fixed ebuild!  

Security, please vote on GLSA.

B2 doesn't call a vote. Only A4, B3, B4, C3 do... so GLSA there will be.

GLSA 200412-20