mirror of
https://github.com/chipsec/chipsec
synced 2026-06-08 13:31:00 +00:00
Nathaniel Mitchell
99 lines
4.2 KiB
Python
99 lines
4.2 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, BIOS
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from chipsec.library.returncode import ModuleResult
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from chipsec.library.logger import print_buffer_bytes
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from typing import List
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TAGS = [BIOS]
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METADATA_TAGS = ['OPENSOURCE', 'IA', 'COMMON', 'BIOS_KBRD_BUFFER']
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COMMON_FILL_PTRN = ''.join([f'{(chr(x + 0x1E)):1}' 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) -> bool:
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return True
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def check_BIOS_keyboard_buffer(self) -> int:
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kbrd_buf_head = self.cs.hals.memory.read_physical_mem_dword(0x41A) & 0x000000FF
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kbrd_buf_tail = self.cs.hals.memory.read_physical_mem_dword(0x41C) & 0x000000FF
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self.logger.log(f'[*] Keyboard buffer head pointer = 0x{kbrd_buf_head:X} (at 0x41A), tail pointer = 0x{kbrd_buf_tail:X} (at 0x41C)')
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bios_kbrd_buf = self.cs.hals.memory.read_physical_mem(0x41E, 32)
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self.logger.log('[*] Keyboard buffer contents (at 0x41E):')
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print_buffer_bytes(bios_kbrd_buf)
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bios_kbrd_buf = bios_kbrd_buf.decode('latin_1')
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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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self.result.setStatusBit(self.result.status.SUCCESS)
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return self.result.getReturnCode(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(f'Keyboard buffer tail points inside the buffer (= 0x{kbrd_buf_tail:X})')
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self.logger.log(f' It may potentially expose lengths of pre-boot passwords. Was your password {(kbrd_buf_tail + 2 - 0x1E) // 2:d} characters long?')
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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 do not seem to be exposed.')
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if has_contents:
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self.result.setStatusBit(self.result.status.POTENTIALLY_VULNERABLE)
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return self.result.getReturnCode(ModuleResult.WARNING)
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else:
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self.result.setStatusBit(self.result.status.SUCCESS)
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return self.result.getReturnCode(ModuleResult.PASSED)
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def run(self, module_argv: List[str]) -> int:
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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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