CWE-1246 covers products that do not implement wear leveling for limited-write non-volatile memory, or implement it incorrectly. It matters to anyone designing or integrating devices with NAND flash, EEPROM or similar storage, where an attacker can turn ordinary writes into physical damage.
How it happens
Memories such as NAND flash and EEPROM are split into segments that can each be erased only a limited number of times. Past that limit the device becomes unreliable.
Wear leveling spreads the load. Once a set threshold is reached, writes to a logical block are mapped to a different physical block, so no single block fails early under a heavy write pattern.
If that mechanism is absent or can be bypassed, software that can write repeatedly to one location can wear it out. MITRE shows an attack loop in C++ that allocates one more aligned array than the maximum associativity of the largest cache and then increments an element in each array in an endless loop. Without wear leveling, the targeted memory line fails. MITRE also notes that simple randomization of blocks is not enough, because the randomized physical block is the one that wears out instead.
What an attacker gains
The impact is availability. The record lists denial of service through instability. Attackers may be able to make the storage unreliable in a much shorter time than normal use would take. For a device in the field, that can mean a permanent failure that a reboot does not fix.
How to find it
The record lists no detection methods. A review can ask:
- Which memories on the device have limited write endurance?
- Is wear leveling present for each of them, and is it on the only path to the memory?
- Can untrusted software issue repeated writes to one logical address, and what happens to the physical cells?
- Is wear leveling covered by tests, not only by design intent?
How to fix it
MITRE's mitigation, which applies at design, implementation and testing, is to include secure wear leveling algorithms and make sure they cannot be bypassed. Effectiveness is rated high. The words "secure" and "bypassed" are the important part: an algorithm that an attacker can route around only protects against accidents.
Quick check
What does wear leveling do?
Once a threshold is reached it maps writes from a logical block to a different physical block, which stops one physical block from failing early under concentrated writes.
Why is simple randomization of blocks not enough?
Per the MITRE example, the randomized physical block simply becomes the one that wears out, so the attack still works.
