smaSHeM is a System V shared memory segment manipulator.
Key features
- Allows dumping of segments in a variety of formats including JPEGs
- Allows patching of segments
Overview
System V shared memory segments created with shmget() are assigned an owner, a group and a set of permissions intended to limit access to the segment to designated processes only. The owner of a shared memory segment can change the ownership and permissions on a segment after its creation using shmctl(). Any subsequent processes that wish to attach to the segment can only do so if they have the appropriate permissions. Once attached, the process can read or write to the segment, as per the permissions that were set when the segment was created.
smaSHeM takes advantage of applications that set weak permissions on such segments, allowing an attacker to dump or patch their contents. As discussed in my presentation at 44CON 2013 entitled “I miss LSD“, in the case of many X11 applications it is possible to extract pixmaps of previously rendered GUI artifacts. When compiled with QtCore linking enabled, smaSHeM aids in that process by brute forcing potentially valid dimensions for the raw pixmap dump.
Installation
$ ./configure [--with-qtcore] && make && make install
Usage
$ smaSHeM -v | -i <shmemid> -l <shmemlength> <-@ <patchoffset> -s <patchstring> | -d [-p | -c | -P | -j -x <xstart> -X <endx> -y <starty> -Y <yend>]>
Examples
Dumping the contents of a System V shared memory segment prettily:
$ smaSHeM -i 94273546 -l 459200 -d -P 0xf32fa000 00 00 00 00 1a 1a 1a 1a ........ 0xf32fa008 7d 7d 7d 7d a7 a7 a7 a7 ........ 0xf32fa010 af af af af af af af af ........ 0xf32fa018 af af af af af af af af ........ 0xf32fa020 af af af af af af af af ........ 0xf32fa028 af af af af af af af af ........ 0xf32fa030 af af af af af af af af ........ 0xf32fa038 af af af af af af af af ........ 0xf32fa040 af af af af af af af af ........ 0xf32fa048 af af af af af af af af ........ 0xf32fa050 af af af af af af af af ........ 0xf32fa058 af af af af af af af af ........ 0xf32fa060 af af af af af af af af ........ 0xf32fa068 af af af af af af af af ........ 0xf32fa070 af af af af af af af af ........ 0xf32fa078 af af af af af af af af ........ ...
Patching a segment:
$ smaSHeM -i 41779331 -l 2640 -@ 0 -s `perl -e 'print "A"x1024'`
Dumping the contents of a segment as a set of JPEGs with dimensions 0-300×30 (required QtCore):
$ smaSHeM -i 41779331 -l 2640 -d -J -x 0 -X 300 -y 30 -Y 30
