Bug 201335

Summary: CVE-2006-1168 Possibility to underflow a .bss buffer with attacker controlled data
Product: Red Hat Enterprise Linux 4 Reporter: Marcel Holtmann <holtmann>
Component: ncompressAssignee: Peter Vrabec <pvrabec>
Status: CLOSED ERRATA QA Contact: Ben Levenson <benl>
Severity: low Docs Contact:
Priority: medium    
Version: 4.0CC: security-response-team, sgrubb
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard: impact=low,source=vendorsec,reported=20060725,embargo=20060808,public=20060808
Fixed In Version: RHSA-2006-0663 Doc Type: Release Note
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2006-09-12 16:47:29 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 201919    
Attachments:
Description Flags
fix candidate none

Description Marcel Holtmann 2006-08-04 14:02:31 UTC 
Report from Tavis Ormandy, Google Security Team:

An audit of ncompress version 4.2.4 uncovered a serious security flaw, this loop
in decompress() (~1749, compress42.c) performs no bounds checking, allowing a
specially crafted datastream to underflow a .bss buffer with attacker controlled
data. Some research reveals that the lzw decompressors from gzip and openbsd
(both derived from the same public domain implementation) have already corrected
this flaw, however ncompress shipped by (at least) gentoo, debian, fedora and
suse seem to still be vulnerable.

              while ((cmp_code_int)code >= (cmp_code_int)256)
              { /* Generate output characters in reverse order */
                  *--stackp = tab_suffixof(code);
                  code = tab_prefixof(code);
              }

In my test environment I've been able to successfully overwirte .got and .dtors
with controlled data. The most simple testcase would be:

$ perl -e 'print "\x1f\x9d\x90","\x01"x"2048"' | compress -d

My suggested fix would be adding  `&& stackp >= htabof(0)` to the loop condition.
Comment 1 Peter Vrabec 2006-08-10 10:03:33 UTC 
Created attachment 133926 [details]
fix candidate

I'd like to use this patch, which is based on fix extracted from gzip.
Comment 13 Red Hat Bugzilla 2006-09-12 16:47:29 UTC 
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2006-0663.html