Bug 202693 - CVE-2006-1168 Possibility to underflow a .bss buffer with attacker controlled
Summary: CVE-2006-1168 Possibility to underflow a .bss buffer with attacker controlled
Alias: None
Product: Fedora
Classification: Fedora
Component: ncompress
Version: 6
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Peter Vrabec
QA Contact: Ben Levenson
Whiteboard: impact=moderate,source=vendorsec,repo...
Keywords: Security
Depends On:
TreeView+ depends on / blocked
Reported: 2006-08-15 20:43 UTC by Mark J. Cox
Modified: 2007-11-30 22:11 UTC (History)
1 user (show)

Clone Of:
Last Closed: 2006-08-21 11:32:12 UTC

Attachments (Terms of Use)

Description Mark J. Cox 2006-08-15 20:43:54 UTC
Fix needed for FC6

+++ This bug was initially created as a clone of Bug #201919 +++

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.

-- Additional comment from pvrabec@redhat.com on 2006-08-11 07:46 EST --
fixed in ncompress-4.2.4-45

Comment 1 Peter Vrabec 2006-08-21 11:32:12 UTC
rawhide fixed in ncompress-4.2.4-45
fc5 in ncompress-4.2.4-44.fc5

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