黑客信息网：硬件安全入门（下）
在上一篇文章中，我们通过一个徽章挑战，为读者详细介绍了如何转储Atmel芯片的固件，在本文中，我们将继续为读者演示如何转储更复杂的一个电路板：Belkin N300路由器。
接下来我们要转储的板子是Belkin N300路由器。当前，Belkin是最受欢迎的消费类路由器品牌之一，这意味着与之前的CTF徽章不同，这次的挑战提供了更多的真实场景。因此，在该设备中发现漏洞的话，则可能会影响到全球的家庭。
首先我们要做的就是再去尝试定位一个闪存芯片。这次我们确定的是一款MX25L1606E芯片（图11），相关的参数见
图11 mx25l1606e芯片
接下来，我们将使用Attify Badge（图12）来转储我们的固件，因为Bus Pirate已经“罢工”了。
图12 Attify Badge
引脚输出如下所示：
图13 mx25l1606e示意图
MX25L1606E
Attify Badge
CS
CS
SO
MOSI
GND
GND
VCC
3.3V
SCLK
SCK
SI
MOSI
完成上述操作后，它应该是这样的：
图14 mx25l1606E（已经连接Attify Badge）
由于闪存芯片周围有金属框，所以这块板子上使用SOIC夹的空间有限，因此，这次我们采用了鳄鱼夹。
现在，准备工作已经就绪了，下面我们继续转储这个固件。但是，这次我们将使用名为“flashrom”的实用程序，而不是avrdude，因为我们要处理的是闪存 SPI芯片，而不是Atmel芯片。
首先，我们可以使用下面的命令来确定flashrom是否可以转储我们的芯片：“flashrom -p ft2232_spi:type=232H”。
该命令将尝试自动识别我们的芯片。如果你使用的是Bus Pirate，可以用下面的参数代替传递给-p的参数：“flashrom -p buspirate_spi:dev=/dev/ttyUSB0”。
其中，/dev/ttyUSB0是Bus Pirate连接的串口，读者可以根据需要进行修改。运行该命令后，成功返回如下内容：
flashrom v0.9.9-r1954 on Linux 4.15.0-88-generic (x86_64)
flashrom is free software, get the source code at
Calibrating delay loop... delay loop is unreliable, trying to continue OK.
Found Macronix flash chip "MX25L1605A/MX25L1606E/MX25L1608E" (2048 kB, SPI) on ft2232_spi.
如果芯片识别失败也不要担心，可以用“flashrom -L”在列表中手动找到您的芯片，然后运行下面的命令，看看是否还能读取芯片：“flashrom -p ft2232_spi:type=232H -c MX25L1605A/MX25L1606E/MX25L1608E -r dump.bin”。
其中，-p选项表明我们要使用ft2232编程器（如果使用Bus Pirate，则用上面的-p参数进行相应的替换），-c选项表明我们要转储哪种闪存芯片（本例中是MX25L1606E），-r dump.bin告诉它将内容读入文件dump.bin。如果一切顺利的话，我们应该得到一个有效的固件文件。如果失败的话，则会报错，或者创建一个充满空字节的文件。
当然，这个过程可能需要一段时间，特别是对于较大的芯片；另外，我们可以从数据表中识别尺寸大小。由于MX25L1606E以地址1FFFFF结束，所以，其长度为2097151字节或2MB（图15）。
图15 mx25l1606e的存储器组织结构
这块2MB的芯片用了大约2分钟才完全转储过来。最后，我们很幸运，第一次就成功转储了固件。
iot@attifyos ~> flashrom -p ft2232_spi:type=232H -c MX25L1605A/MX25L1606E/MX25L1608E -r dump.bin
flashrom v0.9.9-r1954 on Linux 4.15.0-88-generic (x86_64)
flashrom is free software, get the source code at
Calibrating delay loop... delay loop is unreliable, trying to continue OK.
Found Macronix flash chip "MX25L1605A/MX25L1606E/MX25L1608E" (2048 kB, SPI) on ft2232_spi.
Reading flash... done.
这时，该binwalk上场了：
iot@attifyos ~> binwalk dump.bin
DECIMAL HEXADECIMAL DESCRIPTION
--------------------------------------------------------------------------------
5440 0x1540 LZMA compressed data, properties: 0x5D, dictionary size: 8388608 bytes, uncompressed size: 85344 bytes
28570 0x6F9A Sercomm firmware signature, version control: 256, download control: 0, hardware ID: "AAZ", hardware version: 0x3200, firmware version: 0x6, starting code segment: 0x0, code size: 0x7310
142352 0x22C10 LZMA compressed data, properties: 0x5D, dictionary size: 8388608 bytes, uncompressed size: 2764800 bytes
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从“Sercomm Firmware Signature”这一行，我们可以看到一个硬件的ID为“AAZ”，它与电路板上的硬件ID完全匹配（图16）。现在，我们就可以继续分析这个固件的漏洞了。请记住，如果我们可以转储固件，我们也可以将自定义固件和后门写入闪存芯片。
图16 硬件标识
如果期间出错的话，最可能的两个原因是引脚没有正确连接，或者（如果引脚已经正确连接）它们正在给SPI芯片供电，使得芯片无法进行转储。第二种情况可能很常见，一般来说，最好的解决方法是用热*对芯片进行脱焊，然后用芯片自行转储固件。如前所述，最好检查一下电缆的长度，以确保故障不是由于电缆太长造成的。
虽然转储这些设备可能需要不少时间，但这可以帮助我们加深对这些设备的工作原理的了解。例如，通过转储Belkin设备的固件，我们可以直接分析源web文件，从而使我们可以更容易识别设备内的远程漏洞并加以利用。
通过利用这些类型的设备的安全漏洞，攻击者可以在受害者的路由器内创建一个后门，并重新路由所有网络流量，窃取受害者的银行和电子商务账户等账户的凭证。了解这些漏洞存在的地方，让我们有机会在它们造成任何重大损害之前修复它们。
在本系列的下一部分，我们将讨论JTAG和UART串行接口，如何访问它们，以及我们可以从中得到什么。
我们可以借助一些工具来成功地转储这些固件，例如：
SOIC Clip:
A device for dumping firmware (Bus Pirate):
Cables and clips:
Additional useful wires:
Bus Pirate用于与SPI串行协议进行交互，以便为我们转储固件。其他可行的替代方案包括Shikra（和Attify Badge（当然，每个工具都有自己的优缺点。但是，Bus Pirate以及被广泛使用，并且有很好的文档，在我看来，它是最容易使用的。但是，Shikra被认为比Bus Pirate更稳定，速度更快，但没有那么多的支持。相比之下，Attify Badge则更易于设置，但同样支持有限。此外，Bus Pirate还提供了一个很好的串行接口，如果你愿意的话，可以很轻松与设备进行手动通信。读者可以根据自己的喜好和条件进行选择。
此外，由于电缆和夹子相当便宜，并且容易买到，因此，我特别推荐这些，因为它们已经为我提供了我迄今为止所需的一切，并且可以很好地夹在针脚上。
