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.
Created attachment 133926 [details] fix candidate I'd like to use this patch, which is based on fix extracted from gzip.
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