Researchers at Carnegie Mellon University, Seagate Technology and Swiss Federal Institute of Technology in Zürich have uncovered a potential flaw in the storage devices that power most cell phones, computers and big data centers around the world. The researchers found that the special chip arrays used to store information are vulnerable to malicious programs which can corrupt data and even destroy the chips over time.
NAND flash memory chips installed on a board array are called solid-state drives (SSDs). The SSDs have all but replaced the venerable magnetic disk hard drives, allowing manufacturers to reduce the size and weight of electronic devices. NAND flash memory chips are found inside most of the current state of the art electronics and often occupy space in our pockets from portable phones, cameras, and USB drives. They are also the heart of massive data centers that power the cloud, holding vast amounts of data for individuals, major corporations, and government.
A key feature of the NAND flash chip is its ability to store a charge without power. The NAND chip contains billions of cells each with different electrical charges which represent the binary ones and zeros that make up data. They are also controlled by an internal architecture which is designed to keep all that data in order. The researchers, working with the assistance of Intel and Seagate, found that the cells inside each chip can be corrupted by programs which abuse the sub-scale electronics and can eventually render them useless.
Once such exploit discovered by the researchers is a program that rapidly writes, reads and resets data inside a NAND storage chip. The attacker repeatedly performs this series of attacks against individual chip cells holding the binary ones and zeros, causing them to overload and generate interference against other nearby “victim” cells inside the chip. The result is a phenomenon called “Parasitic Capacitance Coupling” which changes the voltage in adjacent memory cells and thereby changes the value of the data stored inside them. The attacker can alter the data stored in targeted victim cells thus data stored by other programs is now corrupted.
As chips become smaller and more powerful, the space between the electronic connections and memory cells has been reduced as well. The fact that these electronic connections are in some cases only a few molecules apart is like having bare copper wires carrying voltage lying next to each other. They often do not have to touch to create disturbance in other nearby components.
This type of interference attack has been described to be similar to a “Row hammer” attack used against the more familiar RAM (Random Access Memory) chips inside computers, where an attacker bombards a row of memory cells in repeated read-write operations, causing electrical interference that changes the values of nearby cells.
“Row hammer” attacks are deliberately introduced interference using software programs. However, Nature can also cause similar errors inside storage memory chips operating under harsh conditions. For example, solar flares and intense radiation have been known to induce the cells inside computer chips – both RAM and Flash – to change values.
Special programming techniques and manufacturing processes called “RAD” hardening had to be introduced for chips installed inside satellites, military equipment, space craft and nuclear reactors to prevent “bit flipping”, changing cell values induced by the Electro-Magnetic Pulse (EMP) of solar flares, and radiation.
According to the researchers, a malicious program can re-create the same kind of EMP electronic interference on a sub-scale. They discovered that such software can take advantage of the NAND chip design and structure to work around safeguards to target specific cells.
While The NAND memory chip can compensate for damaged cells, as more and more cells are attacked, the chip eventually becomes useless and is unable to reliably store information. The attack can dramatically reduce the useable lifetime of the chip, forcing it to be replaced. This replacement process usually would require and entire board or bank of chips to be replaced in high-end applications such as cloud memory, an expensive and time-consuming process.
However, unlike massive cloud and computer storage arrays, the NAND flash memory chips inside consumer devices are usually not replaceable. The malicious software attack could force an entire device to be replaced such as a cell phone, notepad computer or Internet of Things device.
Researchers also discovered a second method of attack called “Read Disturb”. The attack is characterized by a malicious application to quickly perform a large number of reads in a very short amount of time, to induce “Read Disturb” errors that corrupt both data already written to the chip and data that have yet to be written. The basic concept is to corrupt unwritten blocks or cells which are not managed by the chip structure programming. The result is the un-used data cells are corrupted and cannot be repaired because they are outside of the chip management and control.
While the second level of attack does not disrupt already written data by other programs it does eventually destroy the chip and reduce its lifetime of use.
The researchers also suggested their own form of “RAD” hardening in order to reduce the chance of attacks and increase the lifetime of the NAND flash chips. The best solution was to internally buffer data being read and written to the NAND flash drive itself. The concept is that the buffer will absorb all the read and write activity and then place the data correctly into each NAND memory cell. While this method would consume additional overhead in time, up to 15%, and an additional 2 MB of storage, it would also eliminate the chip vulnerability to being corrupted by either the “Capacitance Coupling” or the “Read Disturbance” attacks.
The research paper – titled “Vulnerabilities in MLC NAND Flash Memory Programming: Experimental Analysis, Exploits, and Mitigation Techniques” is available at:
Charles R. Smith is CEO of Softwar Inc. a US based information warfare company and a former national security journalist. You can find Softwar at https://www.softwar.net
About the author: Charles R. Smith is CEO of Softwar Inc. a US based information warfare company and a former national security journalist.
(Security Affairs – NAND flash chips, hacking)