[Bug-wget] bug / security concern

[A.K. Zidani]

Hello there,

I'm a security researcher and I think I found something interesting when
using wget to download a file under Windows's BASH environment.

here is a quick poc I created:
https://addaxsoft.com/poc/AAAAAAAAA%bb%e4%b8%ad%e7AAAAAAAAAAAAAAAA
when you wget that file; wget will crash at:

Program received signal SIGSEGV, Segmentation fault.
__memset_avx2 () at ../sysdeps/x86_64/multiarch/memset-avx2.S:161

   0x00007ffffe202ae6 <+374>:   sub    rax,rdx
   0x00007ffffe202ae9 <+377>:   vzeroupper
   0x00007ffffe202aec <+380>:   ret
   0x00007ffffe202aed <+381>:   nop    DWORD PTR [rax]
   0x00007ffffe202af0 <+384>:   sub    rcx,0xffffffffffffff80
   0x00007ffffe202af4 <+388>:   vmovd  eax,xmm0
=> 0x00007ffffe202af8 <+392>:   rep stos BYTE PTR es:[rdi],al
   0x00007ffffe202afa <+394>:   mov    rax,rsi
   0x00007ffffe202afd <+397>:   sub    rax,rdx
   0x00007ffffe202b00 <+400>:   vzeroupper
   0x00007ffffe202b03 <+403>:   ret

registers:
(gdb) info registers
rax            0x20202020       538976288
rbx            0xffffffffffffffff       -1
rcx            0xffffffffffff5387       -44153
rdx            0xffffffffffffffff       -1
rsi            0x84b1387        139137927
rdi            0x84bc000        139182080
rbp            0x84b1140        0x84b1140
rsp            0x7ffffffed558   0x7ffffffed558
r8             0x0      0
r9             0x1      1
r10            0x7ffffffed4a8   140737488278696
r11            0x8279880        136812672
r12            0x7      7
r13            0x7      7
r14            0x82798f0        136812784
r15            0x84b1388        139137928
rip            0x7ffffe202af8   0x7ffffe202af8 <__memset_avx2+392>
eflags         0x10287  [ CF PF SF IF RF ]
cs             0x33     51
ss             0x2b     43
ds             0x0      0
es             0x0      0
fs             0x0      0
gs             0x0      0

rdi is accessing inaccessible memory which the cause of the crash:
(gdb) x $rdi
0x84bc000:      Cannot access memory at address 0x84bc000

here is my wget -V output:
root@PC:~# wget -V
GNU Wget 1.17.1 built on linux-gnu.

+digest -gpgme +https +ipv6 +iri +large-file -metalink +nls +ntlm
+opie -psl +ssl/openssl

Wgetrc:
    /etc/wgetrc (system)
Locale:
    /usr/share/locale
Compile:
    gcc -DHAVE_CONFIG_H -DSYSTEM_WGETRC="/etc/wgetrc"
    -DLOCALEDIR="/usr/share/locale" -I. -I../../src -I../lib
    -I../../lib -Wdate-time -D_FORTIFY_SOURCE=2 -I/usr/include
    -DHAVE_LIBSSL -DNDEBUG -g -O2 -fPIE -fstack-protector-strong
    -Wformat -Werror=format-security -DNO_SSLv2 -D_FILE_OFFSET_BITS=64
    -g -Wall
Link:
    gcc -DHAVE_LIBSSL -DNDEBUG -g -O2 -fPIE -fstack-protector-strong
    -Wformat -Werror=format-security -DNO_SSLv2 -D_FILE_OFFSET_BITS=64
    -g -Wall -Wl,-Bsymbolic-functions -fPIE -pie -Wl,-z,relro
    -Wl,-z,now -L/usr/lib -lpcre -luuid -lssl -lcrypto -lz -lidn
    ftp-opie.o openssl.o http-ntlm.o ../lib/libgnu.a

Copyright (C) 2015 Free Software Foundation, Inc.
Licence GPLv3+: GNU GPL version 3 or later
<http://www.gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Originally written by Hrvoje Niksic <address@hidden>.
Please send bug reports and questions to <address@hidden>.





I didn't look into this further, but potentially I can have a memory write
if I get control of rdi and rax at some point in the code path, which may
lead to code execution as well.

NOTE: this only crashes wget running in bash in a Windows environment.
not sure if this is the same as CVE-2019-5953, but I would like to
investigate further.




-- 
imAK.xyz