mirror of
https://github.com/chipsec/chipsec
synced 2026-06-08 13:31:00 +00:00
Aaron Frinzell
94 lines
4.0 KiB
Python
94 lines
4.0 KiB
Python
# CHIPSEC: Platform Security Assessment Framework
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# Copyright (c) 2010-2020, Intel Corporation
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#
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# This program is free software; you can redistribute it and/or
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# modify it under the terms of the GNU General Public License
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# as published by the Free Software Foundation; Version 2.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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#
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# Contact information:
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# chipsec@intel.com
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#
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"""
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Checks for exposure of pre-boot passwords (BIOS/HDD/pre-bot authentication SW) in the BIOS keyboard buffer.
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Reference:
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- DEFCON 16: `Bypassing Pre-boot Authentication Passwords by Instrumenting the BIOS Keyboard Buffer <https://www.defcon.org/images/defcon-16/dc16-presentations/brossard/defcon-16-brossard-wp.pdf>`_ by Jonathan Brossard
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Usage:
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``chipsec_main -m common.bios_kbrd_buffer``
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Examples:
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>>> chipsec_main.py -m common.bios_kbrd_buffer
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"""
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from chipsec.module_common import BaseModule, ModuleResult, MTAG_BIOS
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from chipsec.logger import print_buffer
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TAGS = [MTAG_BIOS]
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COMMON_FILL_PTRN = "".join( ['{:1}'.format((chr(x + 0x1E))) for x in range(32)] )
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class bios_kbrd_buffer(BaseModule):
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def __init__(self):
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BaseModule.__init__(self)
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def is_supported(self):
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return True
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def check_BIOS_keyboard_buffer(self):
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kbrd_buf_head = self.cs.mem.read_physical_mem_dword(0x41A) & 0x000000FF
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kbrd_buf_tail = self.cs.mem.read_physical_mem_dword(0x41C) & 0x000000FF
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self.logger.log( "[*] Keyboard buffer head pointer = 0x{:X} (at 0x41A), tail pointer = 0x{:X} (at 0x41C)".format(kbrd_buf_head, kbrd_buf_tail) )
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bios_kbrd_buf = self.cs.mem.read_physical_mem(0x41E, 32)
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self.logger.log("[*] Keyboard buffer contents (at 0x41E):")
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bios_kbrd_buf = bios_kbrd_buf.decode('latin_1')
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print_buffer(bios_kbrd_buf)
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has_contents = False
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if COMMON_FILL_PTRN == bios_kbrd_buf:
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self.logger.log_good("Keyboard buffer is filled with common fill pattern")
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return ModuleResult.PASSED
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for x in bios_kbrd_buf:
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if ("\x00" != x) and ("\x20" != x):
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has_contents = True
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break
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if (0x1E < kbrd_buf_tail) and (kbrd_buf_tail <= 0x1E +32):
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self.logger.log_bad( "Keyboard buffer tail points inside the buffer (= 0x{:X})".format(kbrd_buf_tail) )
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self.logger.log( " It may potentially expose lengths of pre-boot passwords. Was your password {:d} characters long?".format((kbrd_buf_tail +2 - 0x1E) //2) )
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self.logger.log("[*] Checking contents of the keyboard buffer..\n")
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if has_contents:
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self.logger.log_warning("Keyboard buffer is not empty. The test cannot determine conclusively if it contains pre-boot passwords.")
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self.logger.log(" - The contents might have not been cleared by pre-boot firmware or overwritten with garbage.")
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self.logger.log(" - Visually inspect the contents of keyboard buffer for pre-boot passwords (BIOS, HDD, full-disk encryption).")
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else:
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self.logger.log_passed("Keyboard buffer looks empty. Pre-boot passwords don't seem to be exposed")
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return (ModuleResult.WARNING if has_contents else ModuleResult.PASSED)
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# --------------------------------------------------------------------------
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# run( module_argv )
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# Required function: run here all tests from this module
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# --------------------------------------------------------------------------
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def run( self, module_argv ):
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self.logger.start_test("Pre-boot Passwords in the BIOS Keyboard Buffer")
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self.res = self.check_BIOS_keyboard_buffer()
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return self.res
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