Red Hat Bugzilla – Bug 162392
CAN-2005-2096 zlib buffer overflow
Last modified: 2008-01-29 06:02:57 EST
+++ This bug was initially created as a clone of Bug #162391 +++
This is text comes from Mark Adler
The problem was that my previous check for an incomplete code set was much
too liberal. It allowed the passage of pathological code descriptions,
such as a single code of length 10, like what's in zlib-testcase.gz
(twice). The deflate spec allows for distance codes with a single code,
but in that case that single code must have length 1. The patch below now
permits incomplete codes only if they consist of a single code of length
1. Though the spec only mentions distance codes in this regard, my patch
also allows literal/length codes with a single code, which would permit a
dynamic block that only defines the end-of-block code. This should be
permitted by the spec, and it won't crash the code, so I'm letting it
The consequence of letting pathological code descriptions through was that
filling out the decoding table with invalid code markers overran the
ENOUGH sized array and overwrote some other stuff in memory (whatever
happened to follow the inflate state). I thought that I had prevented
that with a check on how much of ENOUGH was being used by the
literal/length code, and knowing the maximum that could possibly be used
by a distance code based on an exhaustive search (MAXD). However my
exhaustive search only included valid distance code sets, and so
zlib-testcase.gz overran MAXD, after a similar pathological literal/length
code set had used most of ENOUGH - MAXD. The patch now only allows valid
code sets through, which are either exactly complete code sets or code
sets that consist of a single code of length 1.
This issue should also affect FC3.
Please see the parent bug for all the details.
Can we get some FC updates for this issue soon?
There are fixed versions for devel (zlib-184.108.40.206-4), fc4 (zlib-220.127.116.11-4.fc4)
and fc3 (zlib-18.104.22.168-2.fc3).
Oh, mistake - fc3 version is zlib-22.214.171.124-2.fc3
Following the paper from Florian Weimer:
and scanning an up to date FC4-install, it reported:
- restore, modprobe, modinfo, depmod
from FC4 to still contain a statically linked version against an old zlib. If
somebody could confirm, would it be possible to please compile new releases?
modprobe, modinfo, depmod have no security context (if you have a malcious
kernel module you're about to load it doesn't really matter if it can exploit
you by zlib). restore/dump similarly.
rsync includes version 1.1.4 of zlib and is therefore unaffected by this issue.